# gst: falling viscoelastic liquid films on a slippery substrate.

<< This (AA) study develops a weighted-residual model for Oldroyd-B films on slippery substrates at moderate Reynolds number and large slippery length. >>

<< Linear stability analysis reveals that wall slip promotes perturbation growth rates, increases cut-off wave numbers, and accelerates long-wave propagation speed, demonstrating a destabilizing effect. Two distinct families of traveling waves are sought, which demonstrate that varying the slippery length can alter the bifurcation type of traveling wave families. >>

<< Particularly, large slippery length can cause the transition of drag-gravity regime into the drag-inertia regime. In the drag-gravity regime, slippery effect promotes the wave speed and height. However, in the drag-inertia regime, slippery effect can suppress the wave height even though the wave propagates faster. >>

<< Interestingly, plateau-type waves (They)  found in the Oldroyd-B film flow at large slippery length, which has not been reported previously. >>

Zhiwei Song, Zijing Ding. Falling viscoelastic liquid films on a slippery substrate. Phys. Rev. E 112, 025106. Aug 25, 2025. 

https://journals.aps.org/pre/abstract/10.1103/vv3p-cvk2

Also: slipping, waves, instability, transition,   in https://www.inkgmr.net/kwrds.html 

Keywords: gst, slipping, slippery substrates, waves, instability, instability of free-surface flows, transitions.

# gst: noisy active matter

<< ️Noise threads every scale of the natural world. Once dismissed as mere background hiss, it is now recognized as both a currency of information and a source of order in systems driven far from equilibrium. >>

<< ️From nanometer-scale motor proteins to meter-scale bird flocks, active collectives harness noise to break symmetry, explore decision landscapes, and poise themselves at the cusp where sensitivity and robustness coexist. >>

<< ️(AA) review the physics that underpins this paradox: how energy-consuming feedback rectifies stochastic fluctuations, how multiplicative noise seeds patterns and state transitions, and how living ensembles average the residual errors. Bridging single-molecule calorimetry, critical flocking, and robophysical swarms, (They) propose a unified view in which noise is not background blur but a tunable resource for adaptation and emergent order in biology and engineered active matter. >>

Atanu Chatterjee, Tuhin Chakrabortty, Saad Bhamla. Noisy active matter. arXiv:2508.16031v1 [cond-mat.soft]. Aug 22, 2025.

https://arxiv.org/abs/2508.16031

Also: transition, noise, track changes in noise, erratic, random, error, mistake, uncertainty, disorder & fluctuations, walk, walking, dance, jazz, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, transitions, noise, track changes in noise, erratic, random, error, mistake, uncertainty, disorder & fluctuations, deposition (analogy, abstraction), walk, walking, life, dance, jazz. 

# gst: self-propelled particles undergoing cyclic transitions.

<< ️Cyclic transitions between active and passive states are central to many natural and synthetic systems, ranging from light-driven active particles to animal migrations. >>

<< ️Here, (AA) investigate a minimal model of self-propelled Brownian particles undergoing cyclic transitions across three spatial zones: gain, loss, and neutral regions. Particles become active in the gain region, passive in the loss region, and retain their state in the neutral region. By analyzing the steady-state behavior as a function of particle number and the size of the loss region, (They) identify a threshold particle number, below and above which distinct structural changes are observed. >>

<< ️Interestingly, below this threshold, increasing the particle number reduces the state-switching time (the time required for a particle to transition from active to passive and back to active). In contrast, above the threshold, further increases in particle number result in longer switching times. In the subthreshold regime, (They) analytical model predicts structural characteristics and switching dynamics that align well with simulations. Above the threshold, (They) observe an emergent clustering, with particles transitioning from passive to active states in close proximity. >>

Ye Zhang, Duanduan Wan. Self-propelled particles undergoing cyclic transitions. Phys. Rev. Research 7, L032040. Aug 21, 2025.

https://journals.aps.org/prresearch/abstract/10.1103/bxmn-hzwh

Also: particle, transition, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, particle, self-propelled particles, transitions, cyclic transitions. 

# gst: dynamics and frictional dissipation for treading slowly in a puddle.

<< ️The process of producing a liquid column is common in daily life and industrial applications, such as walking through a puddle and roller printing. While governed by the Navier-Stokes equation, its dynamics are often studied by numerical means, which hinders a full understanding of the rich mixture of physics behind, for instance, the competition of surface and potential energies, and how the pinch off is affected by the kinetic energy and water jet when a large cylinder is used. For pedestrians rushing out of the rain, the water column inevitably involves turbulence and defies simple theoretical analyses.  >>

<< ️As a result, this (AA) work will focus only on cases with a low Reynolds number to enable laminar flow and the existence of reversible and quasistatic stages. Combined with simple models, (They) elucidate the mechanism that drives the change of morphology and derive analytic expressions for the critical height and upper radius for the liquid column when transiting between three stages. >>

<< ️Stage I is characterized by a static and reversible profile for the column whose upper radius 𝑟𝑡 equals that of the cylinder. The column becomes irreversible and 𝑟𝑡 starts shrinking upon entering stage II. It is not until 𝑟𝑡 stops shrinking that the column neck accelerates its contraction and descends toward the pool, the quantitative behavior of which is among the successful predictions of our theory. Pinch off dominates the second half of stage III without its usual signature of self-similarity. This is discussed and explained with an interesting incident involving a water jet similar to that made by a dropping stone. >>

Chung-Hao Chen, Zong-Rou Jiang, Tzay-Ming Hong. Dynamics and frictional dissipation for treading slowly in a puddle. Phys. Rev. E 112, 025105. Aug 25, 2025.

https://journals.aps.org/pre/abstract/10.1103/7t1g-f3fz

arXiv: 2310.09737v2 [physics.flu-dyn]. May 18, 2024.

https://arxiv.org/abs/2310.09737

Also: walk, walking, in https://www.inkgmr.net/kwrds.html 

Keywords: walk, walking.

# gst: apropos of (unexpected?) transitions; the bizarre role of noise as operational control

<< ️Stochastic systems have a control-theoretic interpretation in which noise plays the role of control. In the weak-noise limit, relevant at low temperatures or in large populations, this leads to a precise mathematical mapping: The most probable trajectory between two states minimizes an action functional and corresponds to an optimal control strategy.  >>

<< ️In Langevin dynamics, the noise term itself serves as the control. For general Markov jump processes, such as chemical reaction networks or electronic circuits, (AA) use the Doi-Peliti formalism to identify the “response” (or “momentum”) field 𝜋 as the control variable. This resolves a long-standing interpretational problem in the field-theoretic description of stochastic systems: Although 𝜋 evolves backward in time, it has a clear physical role as the control that steers the system along rare trajectories. >>

<< ️This implies that nature is constantly sampling control strategies.  >>

<< ️(AA) illustrate the mapping on multistable chemical reaction networks, systems with unstable fixed points, and specifically on stochastic resonance and Brownian ratchets. >>

<< ️ The noise-control mapping justifies agential descriptions of these phenomena and builds intuition for otherwise puzzling phenomena of stochastic systems: why probabilities are generically nonsmooth functions of state out of thermal equilibrium; why biological mechanisms can work better in the presence of noise; and how agential behavior emerges naturally without recourse to mysticism. >>

Eric De Giuli. Noise equals control. Phys. Rev. E 112, 024142. Aug 29, 2025.

https://journals.aps.org/pre/abstract/10.1103/vlx8-spc6

arXiv:2503.15670v3 [q-bio.MN]. 

https://arxiv.org/abs/2503.15670

Also: transition, noise, track changes in noise, erratic, random, error, mistake, uncertainty, disorder & fluctuations, walk, walking, dance, jazz, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, transition, noise, track changes in noise, erratic, random, error, mistake, uncertainty, disorder & fluctuations, deposition (analogy, abstraction), walk, walking, life, dance, jazz. 

# brain: spontaneous emergence of metacognition in neuronal computation.

<< ️Metacognition, a hallmark of human intelligence, enables individuals to assess prediction uncertainty, providing an advantage over artificial intelligence in anticipating risks and performing tasks that demand trustworthiness and reliability. >>

<< ️Here, (AA) demonstrate that metacognition can naturally emerge in recurrent neural networks trained on cognitive tasks without guidance from any probabilistic inference rules or additional network architectures. Through naturally embedded nonlinear coupling with the mean of the network output, the covariance of the network output engages in metacognition by assessing the uncertainty associated with the mean, which represents the task responses. >>

<< ️(AA) further propose testable predictions about how key features of neuronal computation in the brain—noise, neuronal correlations, and heterogeneity—contribute to metacognition. >>

Hengyuan Ma, Wenlian Lu, Jianfeng Feng. Spontaneous emergence of metacognition in neuronal computation. Phys. Rev. Research 7, 033188. Aug 22, 2025.

https://journals.aps.org/prresearch/abstract/10.1103/f1hv-bf1f

Also: brain, network, uncertainty, noise, chaos, in  https://www.inkgmr.net/kwrds.html 

Keywords: gst, brain, cognition, metacognition, learning, memory, networks, biological neural networks, biological information processing, decision making, uncertainty, stochasticity, noise, chaos.

# gst: H.v.Foerster's principle revisited, 'allostasis' theory reconsiders 'order through noise'

<< ️The notion of homeostasis typically conceptualises biological and artificial systems as maintaining stability by resisting deviations caused by environmental and social perturbations. In contrast, (social) allostasis proposes that these systems can proactively leverage these very perturbations to reconfigure their regulatory parameters in anticipation of environmental demands, aligning with von Foerster's ``order through noise'' principle. >>

<< ️This (AA) paper formulates a computational model of allostatic and social allostatic regulation that employs biophysiologically inspired signal transducers, analogous to hormones like cortisol and oxytocin, to encode information from both the environment and social interactions, which mediate this dynamic reconfiguration. >>

<< ️ The (AA) results show that allostatic and social allostatic regulation enable agents to leverage environmental and social ``noise'' for adaptive reconfiguration, leading to improved viability compared to purely reactive homeostatic agents. >>

<< ️This (AA) work offers a novel computational perspective on the principles of social allostasis and their potential for designing more robust, bio-inspired, adaptive systems. >>

Imran Khan. [Social] Allostasis: Or, How I Learned To Stop Worrying and Love The Noise. arXiv: 2508.12791v1 [cs.AI]. Aug 18, 2025. 

https://arxiv.org/abs/2508.12791

Also: noise, transition, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, noise, adaptations, transitions, allostasis, homeostasis, life.