{"id":"79b649e9-8c98-4588-92f4-e9c86c7ae4fb","arxiv_id":"2507.20969","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"In a simulated polydisperse suspension of self-propelled filaments, length disparity stabilizes nested spiral structures in which long filaments wrap around short ones.","lead":"Simulations show that when active semiflexible filaments have mixed lengths, long filaments wrap around short ones and form nested spirals that survive at higher activity than in same-length systems. The result suggests that filament length differences alone can drive hierarchical organization in active matter.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Central claim that polydispersity enables nested-spiral persistence at high Pe rests on cross-paper comparison; no matched monodisperse control appears in this study.","rationale":"The reader's verdict is CONDITIONAL, and I agree that the paper needs revision before full acceptance. Of the two weaknesses the reader identifies, the missing matched monodisperse control is the more load-bearing because the central claim is explicitly comparative: polydispersity is said to extend nested-spiral stability beyond the monodisperse case. The comparison to Refs [22,23] is not a control; those studies use different parameter choices and model details, so the observed persistence could arise from those differences rather than from length disparity. The r_bar threshold concern is real but secondary: even if the threshold were perfectly calibrated, it would not establish the comparative claim. My read does not change the verdict; it stays CONDITIONAL, contingent on the authors either providing matched monodisperse simulations or softening the comparative claim. I mark agreement as partial because I focus on the control issue rather than on the threshold as the primary weakness.","tokens_in":10175,"tokens_out":4791,"duration_ms":52030,"concrete_test":"Run matched monodisperse control simulations with the exact same SAMoS parameters as the polydisperse runs (Tether bonds, bending rigidity such that ξp/L = 1.3, WCA, kBT=0.1, γ=1, ρ=0.3, δt=1e-3, same total number of beads N=5e4, same equilibration and averaging protocol) for monodisperse filaments of length Nb = 71 (and optionally Nb = 37, 54) across Pe = 30, 70, 110, 150. Apply the same nested-spiral identification used for the polydisperse case and compute Nnested as a function of Pe. If Nnested remains nonzero at Pe ≥ 110 in the monodisperse control, the central 'persistence due to polydispersity' conclusion fails; if it drops to zero while the polydisperse case retains Nnested>0, the claim is supported.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper's central novelty is that polydispersity 'profoundly alters' nested-spiral stability and promotes 'persistent confinement at high activity' (Section IV), with the abstract stating the collective wrapping mechanism is 'absent in monodisperse systems.' However, the main text contains no monodisperse simulation with the same model and parameters as the polydisperse runs. The persistence comparison is made against Refs [22,23], which use their own interaction potentials, stiffness protocol, packing fraction, filament lengths, and activity definitions. Here the model fixes the persistence ratio ξp/L = 1.3 for all filament lengths, uses a Tether bond potential, ρ=0.3, and a uniform length distribution of 10 discrete lengths. Any of these differences could shift the activity at which monodisperse nested spirals dissolve. If a matched monodisperse control also shows two-filament wrapped structures surviving at high Pe, the claim that length disparity is responsible for the extended stability would be unsupported. The r_bar threshold issue (defined only in the SI) is secondary: even a robust cluster definition would not resolve whether the persistence is due to polydispersity or to model parameters.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports molecular-dynamics simulations of a two-dimensional polydisperse suspension of self-propelled semiflexible filaments with fixed bond lengths and ten discrete filament lengths. The authors compute the per-length average turning number as a function of Péclet number, identify 'nested spirals' through a center-of-mass distance threshold, and analyze filament displacements via self-part van Hove distributions. Their central claims are that length polydispersity preserves the reentrant spiral regime of monodisperse systems, that polydisperse systems exhibit a collective wrapping mechanism absent in monodisperse systems, and that this mechanism stabilizes two-filament nested spirals at high activity, promoting persistent confinement. The paper includes a clear model description, standard simulation methodology, and qualitative snapshots of the proposed wrapping mechanism.","tokens_in":10378,"tokens_out":2944,"duration_ms":36351,"significance":"If the central claims are correct, the paper identifies a new and potentially important mechanism for hierarchical self-assembly in active matter: length disparity alone can stabilize multi-filament wrapped structures beyond the activity range where monodisperse spirals dissolve. The study is also potentially useful as a benchmark because the model is described in enough detail to reproduce, the observables (turning number, Péclet number, van Hove distributions) are direct and not fitted, and the simulation package is identified. However, the load-bearing novelty—'collective wrapping absent in monodisperse systems' and 'persistent confinement at high activity'—is established only by comparison with earlier monodisperse simulations using different model parameters, not by a matched control in this manuscript. The quantitative structural statistics also depend on a threshold defined only in the Supplementary Material, and no error bars are shown for the key averages. These issues must be addressed before the claims can be considered fully supported.","major_comments":[{"comment":"The central claim that polydispersity enables nested spirals to persist at high Péclet numbers is not tested against a monodisperse control in this manuscript. The comparison is made to Refs. [22] and [23], which use different interaction potentials, stiffness protocols, packing fractions, filament lengths, and activity definitions. For example, this paper fixes ξp/L=1.3, uses the Tether bond potential, ρ=0.3, and a uniform length distribution of 10 discrete lengths; any of these choices could shift the activity at which monodisperse nested spirals dissolve. Please add matched monodisperse simulations with the same model, same ρ, same ξp/L, and the same individual filament lengths at the same Péclet numbers, and compare the nested-spiral statistics and turning-number reentrance directly. Without such controls, the abstract's claim that the collective wrapping mechanism is 'absent in monodisperse systems' is not established.","section":"Section IV and Fig. 3"},{"comment":"The identification of nested spirals relies entirely on a threshold distance r̄, stated only as 'provided in the Supplementary Material.' All quantitative trends in Fig. 3—⟨Nf⟩ approaching 2, ⟨lmin/lmax⟩ decreasing toward the minimum ratio, and the two-stage decay of Nnested—depend on this cluster criterion. The manuscript should report the exact value of r̄ in the main text and demonstrate that the reported trends are robust to reasonable variations of r̄ (e.g., a sensitivity analysis over ±20–30%). Without this, a reader cannot assess whether the structural characterization is an artifact of the threshold choice.","section":"Section III B"},{"comment":"Key quantitative claims are made without statistical uncertainty estimates. The average turning number ⟨|ψ|⟩, the nested-spiral statistics ⟨Nf⟩, ⟨lmin/lmax⟩, Nnested, and the van Hove distributions are all plotted without error bars or confidence intervals. The manuscript states that 10 independent simulations are used for the van Hove analysis, but no measure of run-to-run variability is shown. Since the paper's conclusions include shifts in transition Péclet numbers and quantitative comparisons with earlier monodisperse results, the absence of error bars makes it impossible to determine whether the reported differences are significant. Please provide error estimates for all averaged quantities.","section":"Figs. 1, 3, and 4"}],"minor_comments":[{"comment":"The caption refers to 'l = 11' for the short filament case, while the text and legend define lengths by bead number Nb = 11. Please use consistent notation throughout, either Nb or L.","section":"Fig. 4 caption"},{"comment":"The Péclet number is written as 'P e' with a space, and 'P´eclet' appears with an accented character issue. Please use a uniform notation such as 'Pe' throughout.","section":"Section II"},{"comment":"The sentence 'at the Pe where filaments form stable spirals in the monodisperse system, the presence of shorter filaments ... promotes their premature unwinding' is a mechanistic claim that appears only with a pointer to the Supplementary Material. Please provide the supporting data or figure in the main text, or state which supplementary figure is relevant.","section":"Section III A"}],"recommendation":"major_revision","confidential_remarks":"The paper is within the scope of cond-mat.soft and addresses a timely question. The main concern is that the core novelty is a comparison against previously published monodisperse data rather than a matched control. If the authors can supply matched monodisperse simulations and a sensitivity analysis of the nested-spiral threshold, the paper could become a solid contribution. I do not see this as a reject situation, because the simulation protocol is transparent and the qualitative trends are internally plausible; the missing controls and error bars are fixable within a revision."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Short version: this is a competent simulation study of a question that has been sitting in plain sight—what length polydispersity does to active-filament spirals. The mechanism they identify, long filaments wrapping short ones and surviving at higher Pe than monodisperse spirals, is plausible and supported by their snapshots and order parameters. But the central claim is not nailed down by the evidence presented, because the persistence comparison is made against earlier monodisperse simulations with different parameters, not a matched control run with the same model. That is the soft spot that matters.\n\nWhat is genuinely new: systematic polydisperse length distributions in this class of active semiflexible filament models, and the two-filament long-short nested spiral as a persistent high-Pe state. The turning number reentrance by length, the lmin/lmax trend, and the bimodal van Hove distributions are consistent and give a coherent picture. The paper is honest about what is and isn't seen in monodisperse refs, and the simulation protocol is described well enough to reproduce. Credit for that.\n\nWhere it is soft: (1) The headline 'absent in monodisperse' is an overstatement—nested spirals exist in monodisperse systems per Ref [22]; what polydispersity does is extend their lifetime to higher Pe. The abstract should say that. (2) The persistence claim rests on comparing to Refs [22,23], which use different potentials, packing fractions, and activity definitions. A matched monodisperse control at the same ξp/L, rho, and interaction model would settle it. Without that, 'polydispersity causes the persistence' is an inference, not a demonstrated result. (3) The r_bar cluster threshold is only in the SI; that is fine technically, but a robustness check over threshold values would make the statistics in Fig. 3 solid. (4) No error bars on ⟨|ψ|⟩, ⟨Nf⟩, etc. They do average over 10 seeds for van Hove, but not for the structural quantities. That is minor relative to (2), but it is easy to fix.\n\nThe paper deserves a serious referee. The question matters, the simulation approach is sound, and the weakness is addressable without changing the core method. Send it to review, ask for a matched monodisperse control and error bars, and the result will be much stronger.","headline":"Solid simulation study with a plausible new mechanism, but the persistence claim needs a matched monodisperse control before it is fully sold.","tokens_in":10945,"tokens_out":2278,"would_cite":true,"duration_ms":23006,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Polydispersity in filament length turns single-filament spiraling into cooperative wrapping: long active filaments coil around shorter ones, forming nested spirals that persist at activities where monodisperse nested structures dissolve.","keywords":["active filaments","polydispersity","nested spirals","self-propelled semiflexible polymers","turning number","van Hove distribution","collective wrapping","nonequilibrium self-assembly"],"falsifier":"Run this model at the same packing fraction, stiffness, and activity window with a strictly monodisperse length distribution under identical simulation settings, and count nested spirals with the same $\\bar{r}$ criterion; if the polydisperse system does not retain significantly more nested spirals at high $\\mathrm{Pe}$, the persistence claim fails. Independently, sweep $\\bar{r}$ across the values consistent with the Supplementary Material: if the two-stage decay in the number of nested spirals and the $\\langle l_{\\min}/l_{\\max}\\rangle$ trend are not stable to the threshold choice, the structural transition is an artifact of the cluster criterion.","tokens_in":9963,"feed_emoji":"🌀","tokens_out":4492,"duration_ms":44296,"temperature":0.7,"pith_summary":"This paper asks whether length polydispersity changes how self-propelled semiflexible filaments organize in two dimensions. It argues that it does: when filaments come in different lengths, longer ones coil around shorter ones and trap them, forming 'nested spirals' that are stable at activity levels where the nested structures seen in monodisperse systems have already fallen apart. The mechanism is length disparity itself, not any added attraction, so the paper identifies filament length as a control parameter for nonequilibrium self-assembly. A careful reader would care because real cytoskeletal and bacterial filament systems are naturally polydisperse, and this gives a minimal route to hierarchical, cooperative confinement in active matter.","feed_headline":"Mixed-length filaments wrap into spirals that outlast monodisperse ones","feed_subtitle":"Simulations show length disparity alone lets active filaments form nested spiral clusters that monodisperse systems lose at high activity.","key_machinery":"The central object is the nested spiral: a cluster of filaments whose centers of mass all lie within a threshold distance $\\bar{r}$ (defined in the Supplementary Material). The paper measures it with the turning number $\\psi = (1/2\\pi)\\sum_j (\\theta_{j+1}-\\theta_j)$, which counts how many turns a filament makes, and with the self-part of the van Hove distribution of filament center-of-mass displacements, which separates confined from motile populations. These tools together carry the argument: turning number shows length-dependent reentrant spiraling, nested-spiral statistics show the transition from multi-filament to two-filament structures, and the van Hove distribution shows the dynamical signature of confinement.","core_discovery":"In a two-dimensional, dry suspension of active semiflexible filaments with fixed bond lengths and ten discrete lengths, the authors find a collective wrapping mechanism absent in monodisperse systems. At intermediate Péclet number, long filaments wind around shorter ones, producing nested spirals; as activity rises, medium filaments unwind first, leaving two-filament structures of one long filament wrapped around one short filament, and only at still higher activity do these break down. The turning number per filament length shows the same reentrant open-chain/spiral/open-chain behavior as the monodisperse case, but with length-dependent thresholds, so polydispersity shifts when each population transitions and extends the lifetime of nested spirals. The van Hove displacement distributions at $\\mathrm{Pe}=110$ are bimodal for short and medium filaments, reflecting coexisting confined and motile populations, and single-peaked for long filaments, which remain trapped in spirals.","pith_inferences":["Because the mechanism is purely steric and length-based, the same wrapping should appear in other rod-like active particles, granular rods, or colloidal chains whenever a length distribution overlaps with a broad activity window; this could be tested in experiments with mixtures of two rod lengths.","The paper's 'nested spiral' definition only uses centers of mass; a topological measure of mutual entanglement, such as linking or winding numbers between filament pairs, might reveal whether the two-filament states are genuinely interlocked or merely coaxial, and would make the persistence claim sharper.","Length-dependent propulsion, which the paper suggests as an extension, may reinforce or erase the wrapping depending on whether longer filaments move faster or slower; that is a testable prediction for future simulations.","The exponential length distribution test reported as qualitatively similar suggests that the wrapping is not an artifact of the specific uniform mix, but the threshold $\\bar{r}$ should be re-derived for each distribution before comparing."],"forward_implications":["Polydispersity alone can stabilize multi-filament spiral assemblies at activities where monodisperse systems have already unwound.","The number of filaments per nested spiral drops from many to two as activity increases, and the surviving pairs are strongly length-asymmetric, so filament length disparity becomes the organizing variable.","van Hove distributions predict coexisting fast, motile filaments and confined, spiral-trapped filaments within the same system, with the split depending on filament length.","The same reentrant spiral behavior seen in monodisperse systems survives polydispersity, but with length-dependent Péclet thresholds, so polydispersity can both destabilize (premature unwinding of medium filaments) and stabilize (wrapping of short filaments by long ones)."],"supporting_citations":[{"why":"Supplies the single-filament spiral state from which the paper generalizes to cooperative wrapping.","marker":"[21]"},{"why":"Provides the monodisperse nested-spiral result that the paper compares against for persistence.","marker":"[22]"},{"why":"Defines the monodisperse reentrant spiral-to-open transition whose thresholds polydispersity shifts.","marker":"[23]"},{"why":"Supplies the semiflexible filament model with harmonic bending potential and active beads used in the simulations.","marker":"[24]"},{"why":"Introduces the polydisperse active Brownian chain system with the exponential length distribution used as a robustness check.","marker":"[37]"},{"why":"Defines the turning number used to quantify spiral and open-chain conformations.","marker":"[45]"},{"why":"Defines the nested-spiral identification criterion and the threshold value $\\bar{r}$.","marker":"[46]"}],"fun_headline_variants":["Length disparity enables nested spiral wrapping in active filaments","Polydisperse active filaments coil into spirals via length mismatch","Nested spirals form only when filament lengths differ","Length diversity lets active filaments wrap cooperatively","Active polydisperse filaments show collective spiral nesting"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The identification of nested spirals depends on a threshold distance $\\bar{r}$ that is specified only in the Supplementary Material, and the claim that these structures persist longer than in monodisperse systems is compared against earlier published simulations rather than a matched control simulation in this paper; if the threshold or the comparison parameters differ, the reported trends could change.","fun_headline_variants_meta":{"raw":{"variants":["Length disparity enables nested spiral wrapping in active filaments","Polydisperse active filaments coil into spirals via length mismatch","Nested spirals form only when filament lengths differ","Length diversity lets active filaments wrap cooperatively","Active polydisperse filaments show collective spiral nesting"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000591,"raw_usage":{"total_tokens":2748,"prompt_tokens":899,"completion_tokens":1849,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":515,"completion_tokens_details":{"reasoning_tokens":1773}},"tokens_in":515,"tokens_out":1849,"duration_ms":16525,"temperature":1.0,"reasoning_tokens":1773,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T13:03:57.311399+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Run this model at the same packing fraction, stiffness, and activity window with a strictly monodisperse length distribution under identical simulation settings, and count nested spirals with the same $\\bar{r}$ criterion; if the polydisperse system does not retain significantly more nested spirals at high $\\mathrm{Pe}$, the persistence claim fails. Independently, sweep $\\bar{r}$ across the values consistent with the Supplementary Material: if the two-stage decay in the number of nested spirals and the $\\langle l_{\\min}/l_{\\max}\\rangle$ trend are not stable to the threshold choice, the structural transition is an artifact of the cluster criterion.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the single-filament spiral state from which the paper generalizes to cooperative wrapping."},{"cited_title":"Duman, R","cited_arxiv_id":null,"evidence_quote":"Provides the monodisperse nested-spiral result that the paper compares against for persistence."},{"cited_title":"Janzen and D","cited_arxiv_id":null,"evidence_quote":"Defines the monodisperse reentrant spiral-to-open transition whose thresholds polydispersity shifts."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the semiflexible filament model with harmonic bending potential and active beads used in the simulations."},{"cited_title":"Landi, J","cited_arxiv_id":null,"evidence_quote":"Introduces the polydisperse active Brownian chain system with the exponential length distribution used as a robustness check."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Defines the turning number used to quantify spiral and open-chain conformations."}],"review_version":1}