arXiv subjects

Saad Bhamla

Publications and source records attributed to Saad Bhamla.

14 recordsLinked to original sources

arXiv2026

Sensing, Traffic, and Construction in Termites

Subterranean and mound-building termites excavate, transport, and build within the same granular substrate that later regulates how they sense, move, and deposit material. From antennal-scale contacts through body-scale traffic to meter-scale architecture, this review synthesizes three linked problems: how workers sense local geometry and physical cues during search and excavation; how traffic moves through narrow, evolving conduits; and how excavation and deposition remodel the substrate that guides later behavior. Across these length scales, noisy local interactions couple sensing, transport, and construction through a shared material medium, leading to emergent order at the colony scale. We emphasize what is established experimentally, where evidence remains sparse or limited to a few model systems, and how emerging imaging, tracking, and modeling tools are making these feedbacks quantitatively accessible. We use this synthesis to motivate a quantitative physics-of-life framework for termite colonies that continually rewrite the medium through which they sense, move, and build.

physics.bio-ph↗

arXiv2026

Acceleration-based clustering reveals frequent gait switching in sprint sled dogs

Continuous video is difficult to obtain during field studies of sprint sled dogs, limiting analysis of stride-to-stride variation during load-pulling gallop. We developed an acceleration-based pipeline to identify recurrent stride states from harness-mounted tri-axial accelerometers without manual gait labels. Using multivariate dynamic time warping, manifold embedding, and density-based clustering, we analyzed more than 20,000 strides from a 10-dog team and identified recurrent, dog-specific stride states. In one previously annotated individual, acceleration-derived states were broadly consistent with manually labeled gallop patterns. Across dogs, transitions between stride states were frequent, with substantial inter-individual variation and limited evidence of strong team-level coordination. A simple logistic model based on local tugline-force timing and magnitude had weak predictive power for transition events. These results suggest that sprint sled dog gallop occupies a variable set of nearby stride states and that local tugline-force fluctuations alone do not explain the observed switching.

physics.bio-ph↗

arXiv2026

Multi-objective Bayesian optimization of rigid and flexible nozzles for energy-efficient pulsed jet propulsion

The biomechanics of pulsed-jet propulsion in aquatic animals, including squids and jellyfish, provide valuable insights into energy-efficient locomotion. In these organisms, flexible funnel deformation enables rapid acceleration and maneuverability while minimizing energy use. Drawing inspiration from these biological systems, this study investigates performance trade-offs between rigid and flexible nozzle geometries in pulsed-jet propulsion systems. A multi-objective Bayesian optimization framework integrated with three-dimensional fluid-structure interaction (FSI) simulations identifies nozzle designs that maximize hydrodynamic impulse and minimize jet energy input. The optimization reveals fundamentally distinct performance characteristics for rigid and flexible nozzles. Rigid nozzles achieve the highest impulse amplification, up to 5 times that of a baseline cylindrical nozzle, but at substantially increased energy expenditure. In contrast, flexible nozzles yield lower peak impulse enhancement of about 2.5 times while achieving significantly greater propulsion efficiency. The maximum normalized impulse-to-energy ratio for flexible nozzles is about 1.8 times higher than that of rigid configurations, indicating more effective conversion of input energy into useful propulsive output. Analysis of the flow physics shows that optimized rigid nozzles enhance performance through geometry-induced internal entrainment, secondary vortex formation, and contraction-driven jet acceleration. This results in stronger vortex circulation and downstream convection. Flexible nozzles use traveling expansion-contraction deformation waves that promote additional entrainment during expansion and accelerate the internally entrained fluid during contraction to improve pressure recovery, reduce pressure-energy expenditure, and mitigate negative pressure impulse contributions.

physics.flu-dyn↗

arXiv2026

Computational and reduced-order modelling of elastic wave-driven impulse enhancement in pulsed jets through passively flexible nozzles

Elastic wave propagation and energy exchange in passively deforming cylindrical nozzles are investigated through three-dimensional, two-way fluid-structure interaction simulations. Flexible nozzles with varying stiffness (Eh = 75 to 500 N/m, E is Young's modulus, h is thickness) are subjected to pulsatile jet inflow at low Reynolds number (Re ~ 4400). Increased flexibility reduces deformation-wave speed following MoensKorteweg scaling, prolonging the expansion phase. This delayed expansion enhances jet entrainment and elastic energy storage while suppressing early shear-layer roll-up and vortex formation. During contraction, released elastic energy increases jet acceleration and vortex formation. For the most flexible nozzle, primary vortex-ring circulation increases by 52%, vortex convection distance by 9%, and peak outlet kinetic energy flux 4.6-fold versus a rigid nozzle, resulting in a 62% increase in total hydrodynamic impulse. A reduced-order model represents the coupled response as a lumped store-and-release oscillator, derived as a single-mode projection of the inviscid one-dimensional wave equation and closed at the exit by two terms: (i) an inertial end correction that adds the external fluid column of length Le = R accelerating with the jet, and (ii) a vortex-radiation damping term, active only during ejection, determined by the discharged-jet momentum theorem. This damping reproduces the post-overshoot velocity decay undamped closures fail to capture. The model predicts the simulated resonance frequency within 6% and momentum impulse within 4% across Eh = 75 to 500 N/m, and recovers energy histories. Outlet kinetic energy flux is predicted within 6% for the three stiffer nozzles and 14% for the most compliant.

physics.flu-dyn↗

arXiv2026

A developmental switch from capillary rectification to elastic catapult enables honeydew ejection in the spotted lanternfly

Plant sap-feeding insects must dispose of excess fluid, yet at millimeter scales droplet release is constrained by capillary adhesion and contact-line pinning. How phloem-feeding insects solve this puzzle, particularly as the excretory apparatus changes in size and form from nymph to adult, has remained unclear. Combining micro-CT, high-speed imaging, measurements of honeydew properties, and reduced-order modeling, we show that the spotted lanternfly (Lycorma delicatula) uses distinct release mechanics across ontogeny. Nymphs release honeydew with an anal stylus that acts as a capillary rectifier, imposing a curvature asymmetry that biases the attached droplet toward detachment through a Laplace-pressure difference. Adults use a longer stylus associated with an elastic basal region, maintain stylus-droplet contact through a finite compression phase, and release droplets with greater translational and rotational momentum. In both stages, stylus rotation is ultrafast, with peak angular accelerations of order $10^7$ rad/s$^{-2}$ and release unfolding on millisecond timescales, yet droplet ejection speed remains below stylus tip speed. Weber-Bond scaling based on measured honeydew properties places both stages at $We_d<1$ and $Bo_d<1$ at the outlet, but distinguishes their post-release states: nymphal droplets remain surface-tension dominated, whereas adult droplets enter deformation- and spin-influenced regimes. Development therefore maintains waste clearance across ontogeny under the same outlet-scale capillary constraint by changing how stylus motion is coupled to the droplet at release, linking life-stage biomechanics to honeydew placement in this invasive phloem feeder and suggesting bioinspired strategies for droplet ejection, antifouling, and self-cleaning surfaces.

physics.bio-ph↗

arXiv2026

Squid-inspired soft superpropulsion

Squid span four orders of magnitude in size yet rely on pulsed jets. We show that the funnel (siphon) is a compliant nozzle whose dilation and recoil lag mantle contraction, storing and returning energy within each pulse, a mechanism we term superpropulsion. Histology reveals a collagen sheath, and chromatophore tracking in two squid species quantifies a repeatable phase lag. Engineered nozzles, 3D fluid-structure simulations, and a reduced-order mathematical model predict > 300% impulse amplification when nozzle response time matches jet acceleration (tau/T = 0.2-0.4), overlapping in vivo timing. Tuned nozzles extend jet reach, enhance plume dispersion, and improve jet-driven boat transport, with gains persisting after 40x miniaturization. Superpropulsion recasts pulsed jets as impedance matching, with a soft nozzle acting as an elastic capacitor that passively shapes impulse delivery in soft robotic thrusters and fluidic actuators.

physics.flu-dyn↗

arXiv2026

Seabird trajectories map onto a reduced optimal-control bound for dynamic soaring

Dynamic soaring allows seabirds to harvest mechanical energy from vertical wind shear, yet there is no common benchmark for comparing flight performance across species based on their trajectories. We derive a reduced lower bound on transport effort from a simplified Hamilton-Jacobi-Bellman optimal-control model in which slow flight incurs an induced-drag penalty, fast flight incurs a dissipative penalty, and wind shear supplies an effective energetic subsidy. \add{We rescale each of the four species to its own baseline speed and accelerometer-based effort, then map them onto a common reduced speed--effort plane and estimate each one's lower frontier. We calibrate the optimal-control bound to one species, the wandering albatross, and test the other three against it. Two further dynamic soarers, the Buller's albatross and short-tailed shearwater, lie progressively above the bound. The common crane, a thermal soarer of comparable body mass, lies about 33 times as far from it as the albatross. Proximity to the boundary, therefore, measures the extent to which a bird's transport is powered by wind shear. More generally, our work offers a framework for testing optimal-control limits in bird flight using field data.

physics.bio-ph↗

arXiv2025

Active polymers translocate faster in confinement

Living organisms employ diverse strategies to navigate confined environments. Inspired by translocation observations on California blackworms (\textit{Lumbriculus variegatus}), we combine biological experiments and active-polymer simulations to examine how confinement and stiffness govern translocation. Active filaments translocate fastest when the channel width is comparable to their diameter, with escape time determined by propulsion speed, filament length, and channel geometry. In wider channels, activity and flexibility induce reorientation-dominated conformational changes that prolong escape. A single dimensionless ratio linking confinement to stiffness captures the transition from axis-aligned escape with short wall deflections for stiffer filaments, to reorientation-controlled motion with blob-like shapes for flexible filaments. These results provide a unified physical framework for active translocation in confinement and suggest design principles for flexible robotic filaments in complex environments.

cond-mat.soft↗

arXiv2025

Semi-automated image analysis of Cellulose Nanofibrils using Machine learning segmentation and Morphological thinning

Reliable and rapid morphology measurement of cellulose nanofibrils (CNFs) with a high level of branching and entanglement is crucial for quality control, grade definition, and investigating morphology-performance relationships in various applications. An image analysis framework, Fibril Analysis for Cellulose Technology (FACT), which utilizes machine learning (ML) segmentation and morphological thinning, was developed to measure the fibril width distribution of cellulose nanofibers (CNFs) from negative contrast scanning electron microscopy (NegC-SEM) images. The high-contrast and wide magnification range of NegC-SEM imaging enabled the capture of micro- and nanoscopic hierarchical branching structures of CNFs. Two ML approaches [Weka and U-Net] were used to create detailed binary segmentation of grayscale NegC-SEM images, critical for the width analysis. Morphological thinning was applied to the binary image to produce a 1-pixel-wide skeleton of the CNF fibril structure. Subsequently, the distance between the skeleton and the original fibril edge was used to calculate fibril width. The FACT framework was optimized and validated with idealized geometric and hierarchical branched structures. FACT effectively performed segmentation, skeletonization, and fibril width measurement of these CNF morphologies. FACT width results were comparable with manual measurements. In the manual method, a single measurement is made per fibril. In contrast, FACT simultaneously makes multiple measurements along each fibril within the entire CNF branched network structure. The advantage of FACT is that complicated branching and network CNF structures can be measured without imparting any analyst bias in fibril selection and measurement. Additionally, once the ML model is trained, each image can be analyzed in under 5 minutes.

physics.bio-ph↗

arXiv2025

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. We 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, we 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.

cond-mat.soft↗

arXiv2025

Gait Transitions in Load-Pulling Quadrupeds: Insights from Sled Dogs and a Minimal SLIP Model

Quadrupedal animals employ diverse galloping strategies to optimize speed, stability, and energy efficiency. However, the biomechanical mechanisms that enable adaptive gait transitions during high-speed locomotion under load remain poorly understood. In this study, we present new empirical and modeling insights into the biomechanics of load-pulling quadrupeds, using sprint sled dogs as a model system. High-speed video and force recordings reveal that sled dogs often switch between rotary and transverse galloping gaits within just a few strides and without any observable changes in speed, stride duration, or terrain, providing clear evidence of locomotor multistability during high-speed load-pulling. To investigate the mechanical basis of these transitions, a physics-based quadrupedal Spring-Loaded Inverted Pendulum model with hybrid dynamics and prescribed footfall sequences to reproduce the asymmetric galloping patterns observed in racing sled dogs. Through trajectory optimization, we replicate experimentally observed gait sequences and identify swing-leg stiffness modulation as a key control mechanism for inducing transitions. This work provides a much-needed biomechanical perspective on high-speed animal draft and establishes a modeling framework for studying locomotion in pulling quadrupeds, with implications for both biological understanding and the design of adaptive legged systems.

eess.SY↗

arXiv2025

Moo-ving mountains: grazing agents drive terracette formation on steep hillslopes

Terracettes, striking, step-like landforms that stripe steep, vegetated hillslopes, have puzzled scientists for more than a century. Competing hypotheses invoke either slow mass-wasting or the relentless trampling of grazing animals, yet no mechanistic model has linked hoof-scale behavior to landscape-scale form. Here we bridge that gap with an active-walker model in which ungulates are represented as stochastic foragers moving on an erodible slope. Each agent weighs the energetic cost of climbing against the benefit of fresh forage; every hoof-fall compacts soil and lowers local biomass, subtly reshaping the energy landscape that guides subsequent steps. Over time, these stigmergic feedbacks concentrate traffic along cross-slope paths that coalesce into periodic tread-and-riser bands, morphologically analogous to natural terracettes. Our model illustrates how local foraging rules governing movement and substrate feedback can self-organize into large-scale topographic patterns, highlighting the wider role of decentralized biological processes in sculpting terrestrial landscapes.

q-bio.QM↗

arXiv2024

A Field Biology Guide for the Curious Physicist

Fieldwork is an essential component not just for organismal biology but also for the expanding umbrella of disciplines that have turned their attention toward the physics of living systems. Observing organisms in nature is a critical component of discovery; however, conducting field research can be a barrier for scientists who do not have experience working with organisms under challenging field conditions. Here, we propose 7 critical steps for organizing and executing interdisciplinary, curiosity-driven field research. Our steps are drawn from insights gained from the in Situ Jungle Biomechanics Lab (JBL), a field research course that helps early-career scientists from both physical and life sciences gain experience in both organizing and conducting interdisciplinary field research in the Amazon Rainforest. We emphasize a curiosity-driven approach towards the scientific inquiry of living systems, one we believe is crucial for discovery while working with wild organisms under highly unpredictable field conditions. We further provide guidance on teamwork when conducting fieldwork, including creating an inclusive environment and advocating for codes of conduct and team structures that aid in conflict resolution. Finally, we outline what we call the in situ approach to fieldwork, one that requires engagements with the environment, scientific community, and local peoples where field sites exist.

q-bio.OT↗

arXiv2024

Temporal network restructuring improves control of indecisive collectives

Controlling multi-agent systems is a persistent challenge in organismal, robotic and social collectives, especially when agents exhibit stochastic indecisiveness -- frequently switching between conflicting behavioral rules. Here, we investigate the control of such noisy indecisive collectives through the lens of century-old sheepdog trials, where small groups of sheep exhibit unpredictable switching between fleeing and following behaviors. Unlike cohesive large flocks, these small indecisive groups are difficult to control, yet skilled dog-handler teams excel at both herding and precisely splitting them (shedding) on demand. Using a stochastic model, we introduce two central parameters -- pressure (stimulus intensity) and lightness (response isotropy) -- to simulate and quantify herding and shedding dynamics. Surprisingly, we find that stochastic indecisiveness, typically perceived as a challenge, can be leveraged as a critical tool for efficient control, enabling controlled herding and splitting of noisy groups. Building on these insights, we develop the Indecisive Swarm Algorithm (ISA) for artificial agents and benchmark its performance against standard algorithms, including the Averaging-Based Swarm Algorithm (ASA) and the Leader-Follower Swarm Algorithm (LFSA). ISA minimizes control energy in trajectory-following tasks, outperforming alternatives under noisy conditions. By framing these results within a stochastic temporal network framework, we show that even with a probabilistic description of the future dynamics, network restructuring (temporality) enhances control efficiency in a specific class of control problems. These insights establish a scalable framework for controlling noisy, behavior-switching collectives, with applications in swarm robotics, cellular engineering, opinion dynamics, and temporal networks.

physics.soc-ph↗