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International Journal of Topology

International Journal of Topology is an international, peer-reviewed, open access journal published quarterly online by MDPI. It focuses on all aspects of topology, including differential topology, algebraic topology, manifolds, and related applications. Its purpose is to provide a platform for the dissemination of research on the various subfields of topology, expand topology to a wider range of applications and, consequently, promote the development of the field.

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All Articles (49)

  • Article
  • Open Access

We develop a self-contained variational calculus for the coordination of synchronised agents. An agent is modelled as an overdamped (Onsager–Machlup) dynamical system on a five-dimensional manifold whose coordinates are an internal Kuramoto order parameter R, a phase variance σ2, and three S-entropy coordinates . Crucially, and in contrast to a preliminary version of this work, every construct used here—the S-entropy coordinates, the partition potential, and the governing Lagrangian—is derived within the paper from three stated axioms (bounded phase space, categorical exclusion, finite resolution); the manuscript depends on no external or unpublished result. We prove (i) a triple-equivalence identity establishing the S-entropy coordinates from maximum-entropy counting; (ii) the explicit Euler–Lagrange equations of the agent action, given in full rather than asserted; (iii) the Kuramoto synchronisation bifurcation, with the corrected critical coupling (for a Gaussian frequency law, ), replacing an erroneous coefficient in the preliminary version; (iv) a formal, analogy-free definition of partition extinction and an observable-commutation theorem that separates functional from ontological indistinguishability; and (v) a coordination calculus for ensembles. We are explicit that the five coordination bands on R are operational classification cut-offs, not phase transitions: the only genuine transition in the model is the Kuramoto bifurcation. Rather than the self-referential numerical checks of the preliminary version, we report nine external experiments against public data (atomic shell structure, the Kuramoto onset by direct simulation, the Wiedemann–Franz constant across eleven metals, sleep-EEG order parameters from PhysioNet, enzyme kinetics, antidepressant meta-analysis, superconductor transport, and representation-disjoint classifiers on a benchmark dataset). Two of these external tests forced corrections to the theory and are reported as such. We are deliberately narrow about applicability: the S-entropy coordinates measure the shape of an agent’s state distribution, not the content or ecological salience of its information; the model is stochastic (Langevin) but single-scale and on a fixed manifold, so it does not represent the multiscale fluctuation and metastability of real biological collectives; and we exhibit a concrete interpretable Lagrangian and a real-data ensemble instance rather than claim to capture any such collective in full. A Scope and Limitations section delimits the defensible claims.

Int. J. Topol.

19 September 2026

Single-Agent State Manifold and Partition Potential. (A) Synchronisation potential 
  
    
      V
      sync
    
    
      (
      R
      ;
      K
      )
    
    =
    
      (
      
        K
        c
      
      −
      K
      )
    
    
      R
      2
    
    /
    2
    +
    K
    
      R
      4
    
    /
    4
  
 on the linear y-axis versus the internal Kuramoto order parameter 
  
    R
    ∈
    [
    0
    ,
    1
    ]
  
 on the linear x-axis, for three coupling regimes: subcritical (
  
    K
    =
    0.5
    <
    
      K
      c
    
    =
    1
  
, steel blue, single minimum at 
  
    R
    =
    0
  
), critical (
  
    K
    =
    
      K
      c
    
  
, seagreen, quartic flat bottom), and supercritical (
  
    K
    =
    3
    >
    
      K
      c
    
  
, crimson, double-well with stable minimum at 
  
    
      R
      *
    
    =
    
      
        1
        −
        
          K
          c
        
        /
        K
      
    
    ≈
    0.816
  
). The pitchfork bifurcation at 
  
    K
    =
    
      K
      c
    
  
 is the only genuine phase transition in the model. Empirical content of Theorem 4 (Synchronisation bifurcation). (B) Variance-floor term 
  
    
      V
      var
    
    
      (
      
        σ
        2
      
      ;
      T
      ,
      K
      )
    
    =
    
      k
      B
    
    T
    
      σ
      2
    
    +
    
      k
      B
    
    T
    /
    
      (
      K
      
        σ
        2
      
      )
    
  
 of the partition potential (Definition 5) on the linear y-axis versus phase variance 
  
    σ
    2
  
 on the linear x-axis, for three coupling strengths 
  
    K
    ∈
    {
    1
    ,
    2
    ,
    4
    }
  
. Each curve has a unique minimum at 
  
    
      σ
      min
      2
    
    =
    
      
        1
        /
        K
      
    
  
 (vertical dashed lines). Higher coupling K produces a lower variance floor. (C) Variance floor scaling figure on log-log axes: 
  
    σ
    min
    2
  
 versus K, six measurement points (steel blue), with theoretical line 
  
    
      σ
      min
      2
    
    =
    
      k
      B
    
    T
    /
    K
  
 (crimson). Slope is exactly 
  
    −
    1
  
 on log-log axes, confirming the analytical prediction. Experiment E05 reports relative error 
  
    1.11
    ×
    
      10
      
        −
        16
      
    
  
. (D) Three-dimensional surface of the partition potential 
  
    Φ
    
      (
      R
      ,
      
        σ
        2
      
      )
    
    =
    
      V
      sync
    
    +
    
      V
      var
    
    +
    
      V
      SF
    
    +
    
      V
      ent
    
  
 over 
  
    
      (
      R
      ,
      
        σ
        2
      
      )
    
    ∈
    
      [
      0.05
      ,
      0.95
      ]
    
    ×
    
      [
      0.1
      ,
      1.5
      ]
    
  
, 
  
    25
    ×
    25
  
 grid, viridis colourmap, fixed 
  
    K
    =
    2
  
, 
  
    
      K
      c
    
    =
    0.5
  
, S-entropy 
  
    S
    =
    (
    0.5
    ,
    0.5
    ,
    0.5
    )
  
. The global minimum lies at 
  
    
      (
      
        R
        *
      
      ,
      
        σ
        min
        2
      
      )
    
    =
    
      (
      0.866
      ,
      0.707
      )
    
  
 (the coherent regime); the surface rises sharply at low 
  
    σ
    2
  
 (variance-floor barrier) and at 
  
    R
    =
    0
  
 (turbulent saddle).
  • Feature Paper
  • Article
  • Open Access

On Regularity via h-Open Sets

  • Saeid Jafari,
  • Lorenzo Affè and
  • Giorgio Nordo
  • + 1 author

We investigate regularity properties defined by means of h-open sets, with systematic use of the associated topology τh=hO(X). In this framework, h-regularity separates points from τ-closed sets by τh-open sets, whereas strong h-regularity is precisely ordinary regularity of . After recalling the established characterization of h-regularity, we obtain preservation results under suitable mappings, study the relation with h∗-regularity and extremal h-disconnectedness, analyze strong -continuity, and establish hereditary results for the regularity notions under the appropriate subspace hypotheses. We also connect the h-R0 condition with the associated topology and with strong h-regularity.

Int. J. Topol.

10 October 2026

  • Article
  • Open Access

More on h-Open Sets

  • Saeid Jafari,
  • Takashi Noiri and
  • Giorgio Nordo
  • + 1 author

We study the topology associated with the family of h-open sets and use it to organize several separation properties in a unified way. After recalling the classical closure, kernel and separation axioms, we distinguish the original topology τ from the associated topology τh=hO(X) and introduce the h-specialization preorder and the h-kernel. The axiom h-R0 is characterized as the natural symmetry property of this preorder and by the equality of singleton h-closures and h-kernels. We prove the relations h-T1⇔h-T0+h-R0 and h-T2⇔h-T0+h-R1, and characterize h-R1 by singleton h-θ-closures. We then develop the theory of h-difference sets and the axioms h-D0, h-D1 and h-D2, proving h-D0⇔h-T0 and h-D1⇔h-D2. A corrected characterization in terms of h-neat points and several preservation results under h-irresolute mappings are obtained. Finally, singleton h-derived sets and h-semisimplicity are related to strong h-regularity.

Int. J. Topol.

23 September 2026

  • Article
  • Open Access

The Standard Model of particle physics has achieved unprecedented success in describing fundamental interactions through the formalism of Quantum Field Theory (QFT), where particles are treated as point-like excitations of underlying fields. In this paper, we introduce an alternative, highly elegant mathematical hypothesis: an effective model that describes particle properties not as fundamental points but as 3D projections of complex topological defects originating in a 4D manifold. By applying the geometry of Kaleidoscopic Iterated Function Systems (KIFS) to a zero-viscosity hydrodynamic framework, we demonstrate a formal isomorphism between standard quantum numbers and 4D fractal attractors. This approach seeks not to replace established phenomenological interactions but rather to offer a complementary geometric lens—a “topological translation”—through which mass generation, spin, and localization can be visualized as emergent properties of higher-dimensional fluid mechanics.

Int. J. Topol.

8 September 2026

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Int. J. Topol. - ISSN 2813-9542