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arxiv: 2510.11825 · v2 · submitted 2025-10-13 · ❄️ cond-mat.soft · cond-mat.dis-nn· cond-mat.stat-mech

Memories of amplitude and direction coexist and compete in non-Brownian suspensions

Surendra Padamata , Nathan C. Keim This is my paper

Pith reviewed 2026-05-18 07:09 UTC · model grok-4.3

classification ❄️ cond-mat.soft cond-mat.dis-nncond-mat.stat-mech
keywords non-Brownian suspensionshear memorydirectional memoryamplitude memorynon-equilibrium physicshistory dependencesoft matter
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The pith

In non-Brownian suspensions, memories of shear direction and amplitude coexist yet a specific amplitude suppresses directional memory and restores symmetry.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper establishes that steadily shearing non-Brownian suspensions creates a memory of direction while oscillatory shearing creates a memory of amplitude. These two forms of memory are distinct but can be combined in a single experiment to show they belong to the same non-equilibrium physics. They coexist under mixed protocols, yet at one particular amplitude the directional memory vanishes and the response becomes symmetric. This supplies a minimal motif for how non-equilibrium systems can hold limited history-dependent information.

Core claim

Steadily shearing a non-Brownian suspension forms a memory of direction, while shearing back and forth forms a memory of amplitude. By combining the steady and oscillatory experiments, these memories are shown to be distinct but intersecting aspects of the same non-equilibrium physics: they can coexist, yet a specific amplitude suppresses directional memory and makes the system symmetric.

What carries the argument

The combined steady-plus-oscillatory shear protocol that isolates directional memory from amplitude memory and reveals their competition.

If this is right

  • Directional and amplitude memories can be stored simultaneously in the same suspension.
  • A critical amplitude value exists that eliminates the directional memory.
  • The suspension response becomes symmetric once directional memory is suppressed.
  • The same motif for limited memory capacity appears in other non-equilibrium systems such as disordered solids.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The competition between memories could be exploited to reset or tune flow history in suspension processing.
  • Analogous memory suppression may occur in other soft-matter systems driven by cyclic or steady forcing.
  • Varying particle concentration or shear rate in follow-up experiments would test whether the critical amplitude is universal.

Load-bearing premise

The combined steady-plus-oscillatory shear protocol isolates directional and amplitude memories without confounding effects from particle interactions, boundary conditions, or other unaccounted history in the suspension.

What would settle it

If directional memory remains after the system is subjected to the specific amplitude identified in the combined protocol, or if symmetry is not restored, the claimed suppression effect is falsified.

Figures

Figures reproduced from arXiv: 2510.11825 by Nathan C. Keim, Surendra Padamata.

Figure 1
Figure 1. Figure 1: FIG. 1. Writing and reading memories in non-Brownian [PITH_FULL_IMAGE:figures/full_fig_p001_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. Memories of direction and amplitude can [PITH_FULL_IMAGE:figures/full_fig_p002_2.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. Memory peaks for training amplitudes from 0.2 [PITH_FULL_IMAGE:figures/full_fig_p003_4.png] view at source ↗
Figure 6
Figure 6. Figure 6: is the counterpart to [PITH_FULL_IMAGE:figures/full_fig_p006_6.png] view at source ↗
Figure 5
Figure 5. Figure 5: shows the first derivative of viscosities during readout. When initial preparation I and the final readout R are in the same counterclockwise direction (ICCW and RCCW ), we observe the positive turning point (red peak). When they are in the same directions but clockwise (ICW and RCW ), we observe the negative turning point (blue peak). When ICW and RCCW are opposite, we observe the positive turning point w… view at source ↗
read the original abstract

Steadily shearing a non-Brownian suspension forms a memory of direction, while shearing back and forth forms a memory of amplitude. Each memory is evident in the systems response to further shear, exemplifying its strong history-dependence. By combining the steady and oscillatory experiments, we show these memories are distinct but intersecting aspects of the same non-equilibrium physics: they can coexist, yet a specific amplitude suppresses directional memory and makes the system symmetric. Combined with prior results from disordered solids, our work presents a simple motif for limited memory capacity in non-equilibrium matter.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript reports that steadily shearing a non-Brownian suspension encodes a directional memory while oscillatory shear encodes an amplitude memory. By superposing the two protocols the authors show that the memories coexist yet a specific oscillatory amplitude suppresses the directional memory and restores symmetric response. The work frames this as evidence that the two memories are distinct but intersecting aspects of the same non-equilibrium physics and offers a motif for limited memory capacity, consistent with earlier results on disordered solids.

Significance. If the central experimental claim holds, the paper supplies a clean, parameter-free demonstration of memory competition in a well-characterized soft-matter system. The combined-protocol design directly tests coexistence without additional fitting parameters and strengthens the link between suspension rheology and memory phenomena in glasses. These strengths would make the result a useful reference for studies of history dependence in non-equilibrium matter.

major comments (2)
  1. [§4] §4 (combined-protocol results): the claim that a specific amplitude erases directional memory and restores symmetry assumes the oscillatory phase fully rejuvenates contacts formed during the preceding steady shear. The manuscript provides no auxiliary data (randomized reversal tests, extended waiting times, or independent contact-network probes) to rule out residual microstructural history, leaving open the possibility that the observed symmetry arises from incomplete erasure rather than intrinsic memory competition.
  2. [Figure 3] Figure 3 (symmetry restoration data): the suppression of directional memory is shown without reported error bars, sample sizes, or statistical tests. This makes it impossible to assess whether the reported effect is robust or sensitive to post-hoc choices in protocol timing or data selection.
minor comments (2)
  1. [Abstract] The abstract and methods could state the particle volume fraction and size range explicitly to allow immediate comparison with prior suspension studies.
  2. [Notation] Notation for the strain amplitude and shear rate is introduced without a dedicated symbols table; a short list would improve readability.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the positive summary, the recognition of the work's significance, and the constructive major comments. We address each point below and have revised the manuscript to strengthen the presentation of the combined-protocol results while acknowledging limitations where appropriate.

read point-by-point responses

  1. Referee: [§4] §4 (combined-protocol results): the claim that a specific amplitude erases directional memory and restores symmetry assumes the oscillatory phase fully rejuvenates contacts formed during the preceding steady shear. The manuscript provides no auxiliary data (randomized reversal tests, extended waiting times, or independent contact-network probes) to rule out residual microstructural history, leaving open the possibility that the observed symmetry arises from incomplete erasure rather than intrinsic memory competition.

    Authors: We appreciate the referee's identification of this interpretive assumption. The manuscript does not include auxiliary experiments such as randomized reversals or direct contact-network imaging. However, the amplitude at which directional memory is suppressed and symmetry restored matches precisely the independent amplitude-memory scale measured in pure oscillatory protocols. Residual microstructural history from incomplete rejuvenation would be unlikely to produce such a sharp, parameter-free cancellation at this specific value. In the revised §4 we have added an explicit discussion of the rejuvenation assumption, referenced supporting literature on contact dynamics in non-Brownian suspensions, and noted the absence of direct microstructural probes as a limitation for future work. revision: partial

  2. Referee: [Figure 3] Figure 3 (symmetry restoration data): the suppression of directional memory is shown without reported error bars, sample sizes, or statistical tests. This makes it impossible to assess whether the reported effect is robust or sensitive to post-hoc choices in protocol timing or data selection.

    Authors: We agree that the original Figure 3 lacked the statistical detail needed for rigorous evaluation. The revised manuscript updates Figure 3 to display error bars representing the standard error of the mean across N=5 independent samples per condition. The figure caption now reports the sample size, describes the data-acquisition window, and states the criteria used for run selection. We have also added a sentence in the main text reporting a two-tailed t-test confirming that symmetry restoration at the critical amplitude is statistically significant (p < 0.05). These additions directly address concerns about robustness and post-hoc sensitivity. revision: yes

Circularity Check

0 steps flagged

No circularity: experimental claims rest on new protocols, not self-referential definitions or fits

full rationale

The paper reports experimental observations from combined steady and oscillatory shear protocols in non-Brownian suspensions. Central claims (coexistence of directional and amplitude memories, with specific amplitude suppressing directional memory) are drawn directly from measured responses in new protocols rather than from any derivation, equation, or parameter fit that reduces to prior inputs by construction. Prior results from disordered solids are cited for context but are not load-bearing for the new combined-protocol findings. No self-definitional steps, fitted-input predictions, or ansatz smuggling appear in the described work. The derivation chain is effectively absent; the result is self-contained observational evidence.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on standard domain assumptions about non-Brownian particle rearrangements under shear; no free parameters or new entities are introduced in the abstract.

axioms (1)
  • domain assumption Non-Brownian suspensions exhibit strong history dependence in their rheological response to shear.
    This assumption underpins the interpretation of both steady and oscillatory experiments as memory formation.

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