Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session T1: Focus Session: Physics of Behavior I |
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Sponsoring Units: DBIO Chair: Greg Stephens, Vrije University Amsterdam Room: 103/105 |
Thursday, March 6, 2014 11:15AM - 11:27AM |
T1.00001: ABSTRACT WITHDRAWN |
Thursday, March 6, 2014 11:27AM - 11:39AM |
T1.00002: Super-resolution Imaging of the Bacterial Chemotaxis System in {\it{Bacillus Subtilis}} Utsav Agrawal, Hanna Walukiewicz, Christopher Rao, Charles Schroeder In this work, we use fluorescence nanoscopy to elucidate a near molecular scale view of proteins involved in bacterial motility. In bacteria, chemotaxis is mediated by receptor clusters that play a key role in response to stimulants, ultimately eliciting a behavioral response as cell motility. Here, we study the chemotaxis system in {\it{B. subtilis}} using stochastic optical reconstruction microscopy (STORM), which enables analysis of nanometer-scale cellular protein assemblies with $\sim$25 nm spatial resolution. We employ STORM to directly visualize dynamic changes in nano architectures of chemotactic receptors (McpB) in response to chemical stimulation. Our work has revealed marked differences in the subcellular localization of receptors upon chemical stimulation in individual cells. We observe that receptor rearrangement is characterized by a largely polar localization in unstimulated cells to a more polar-lateral configuration in cells that have been exposed to ligand. Our work provides crucial information on changes in structure and composition of the polar and lateral receptor clusters in {\it{B. subtilis}} during chemotaxis towards asparagine by quantifying individual molecules, which were previously inaccessible with conventional fluorescence microscopy. [Preview Abstract] |
Thursday, March 6, 2014 11:39AM - 11:51AM |
T1.00003: A simple mapping between cell swimming behavior and single-motor state in multi-flagellated \textit{E. coli} Patrick Mears, Santosh Koirala, Christopher Rao, Ido Golding, Yann Chemla We present new data that resolve a long-standing question on bacterial motility: How does the cell's swimming behavior depend on the number and state of the flagella that propel it? Addressing this question brings us closer to a full understanding of bacterial chemotaxis, arguably still our best paradigm for the way cells modulate their behavior based on signals from the environment. This new is enabled by technical innovation: we combine optical traps, fluorescence microscopy, and microfluidics to simultaneously track the swimming behavior and flagellar rotation state of individual, immobilized \textit{E. coli} cells. We reveal a simple mathematical relationship between the number of flagella on the cell, their rotational bias, and the resulting probability of tumbling. Importantly, inter-flagella correlations result in \textit{E. coli }behaving as if they possess a smaller number of effectively independent flagella than the actual number of flagella. Data from a chemotaxis mutant and stochastic modeling of the network suggest that temporal fluctuations of the key regulator CheY-P are the source of the observed flagellar correlations. A consequence of inter-flagellar correlations is that a cell's run/tumble behavior is only weakly dependent on number of flagella. [Preview Abstract] |
Thursday, March 6, 2014 11:51AM - 12:27PM |
T1.00004: Bacteria as self-propelled liquid crystals: non-equilibrium clustering, polar order, collective motion, and aggregation Invited Speaker: Fernando Peruani Bacteria exhibit fascinating collective phenomena such as collective motion and aggregation. It is usually believed that such kind of collective effects require cells to coordinate their motion via chemotactic signaling. Despite of this common belief, I will show that in experiments with myxobacteria such collective effects emerge in absence of biochemical regulation, and even hydrodynamic interactions, and result from simple physical interaction among the motile bacteria. As proof of principle, I will show that collective phenomena such as collective motion and aggregation naturally emerge in models of simple self-propelled rods that interact by volume exclusion. Combining experiments and theoretical models, we will explain that the interplay of bacterial self-propulsion and steric interactions among the elongated bacteria leads to an effective velocity alignment mechanism (VAM). Such VAM allows cells to display a non-equilibrium clustering transition that marks the onset of collective motion. I will argue that even though the symmetry of the resulting VAM is clearly nematic, it induces, counter intuitively, polar order. Finally, I will show that by increasing the cell density, or alternatively the aspect ratio of bacteria, collective motion patterns become unstable, and cells form aggregates. In short, our results indicate that for bacteria moving on surfaces, the cell shape plays a crucial role in the bacterial self-organization process. By thinking of bacteria as self-propelled liquid crystals, we can explain complex behaviors such as collective motion and aggregation. \\[4pt] References: Peruani and Baer, NJP 15, 056009 (2013); Peruani et al. PRL 108, 098102 (2012); Interface Focus 2, 774 (2012); PRE 74, 030904 (2006). [Preview Abstract] |
Thursday, March 6, 2014 12:27PM - 12:39PM |
T1.00005: ABSTRACT WITHDRAWN |
Thursday, March 6, 2014 12:39PM - 12:51PM |
T1.00006: Sidewinding as a control template for climbing on sand Hamidreza Marvi, Chaohui Gong, Matthew Travers, Nick Gravish, Joseph Mendelson, Ross Hatton, Howie Choset, David Hu, Daniel Goldman Sidewinding, translation of a limbless system through lifting of body segments while others remain in static contact with the ground, is used by desert-dwelling snakes like sidewinder rattlesnakes {\em Crotalus cerastes} to locomote effectively on hard ground, rocky terrain, and loose sand. Biologically inspired snake robots using a sidewinding gait perform well on hard ground but suffer significant slip when trying to ascend granular inclines. To understand the biological organisms and give robots new capabilities, we perform the first study of mechanics of sidewinding on granular media. We vary the incline angle ($0<\theta<20^\circ$) of a trackway composed of desert sand. Surface plate drag measurements reveal that as incline angle increases, downhill yield stresses decrease by 50\%. Our biological measurements reveal that the animals double the length of the contact region as $\theta$ increases; we hypothesize that snakes control this contact to reduce ground shear stress and so avoid slipping. Implementing this anti-slip strategy in a snake robot using contact patch modulation enables the robot to successfully ascend granular inclines. [Preview Abstract] |
Thursday, March 6, 2014 12:51PM - 1:03PM |
T1.00007: Turning and maneuverability during sidewinding locomotion Henry Astley, Daniel Goldman, David Hu Sidewinding is an unusual form of snake locomotion used to move rapidly on yielding substrates such as desert sands. Posteriorly propagating waves alternate between static contact with the substrate and elevated motion, resulting in a ``stepping'' motion of body segments. Unlike lateral undulation, the direction of travel is not collinear with the axis of the body wave, and posterior body segments do not follow the path of anterior segments. Field observations indicate that sidewinding snakes are highly maneuverable, but the mechanisms by which these snakes change direction during this complex movement are unknown. Motion capture data from three Colorado Desert sidewinder rattlesnakes (\textit{Crotalus cerastes laterorepens}) shows a variety of turn magnitudes and behaviors. Additionally, sidewinders are capable of ``reversals'' in which the snakes halts forward progress and begins locomotion in the opposite direction without rotation of the body. Because the head is re-oriented with respect to the body during these reversals, the snake is able to reverse direction without rotation yet continue moving in the new direction without impediment to perception or mechanics, a rare level of maneuverability in animals. [Preview Abstract] |
Thursday, March 6, 2014 1:03PM - 1:15PM |
T1.00008: Pellet formation, manipulation and transport by ants fire in confined environments Daria Monaenkova, Nick Gravish, Rachel Kutner, Michael A.D. Goodisman, Daniel I. Goldman Red imported fire ants, Solenopsis invicta$,$ form colonies of thousands of animals living in complex subterranean nests. Frequent nest relocations in response to flooding require that the ants be excellent excavators. In granular media, the ants excavate soil in the form of pellets composed of several grains and held together by capillary forces. We challenged groups of small and large ants (measured by head width S) to create soil pellets in granular media composed of fine and coarse glass particles mixed with water (W$=$0.01 and 0.1 by mass). In coarse soils (D$=$0.7 mm diam., comparable to S) neither S nor W affected pellet volume; pellets were composed of only one grain. Pellets larger than one grain fell apart during their formation or transport. In fine soils (D$=$0.24 mm diam.) the higher cohesion and smaller D allowed for greater flexibility in pellet formation; pellets were formed from 1 to 22 grains with the median pellet composed of 6 grains. Surprisingly, despite the ability to cohere more strongly, the pellet size did not change as W increased. We hypothesize that although the cohesion allows formation of large pellets in fine particles, the optimal pellet size is controlled by active manipulation and is thus dictated by traffic in the crowded nest. [Preview Abstract] |
Thursday, March 6, 2014 1:15PM - 1:27PM |
T1.00009: Impulsive movements lead to high hops on sand Jeffrey Aguilar, Daniel I. Goldman Various animals exhibit locomotive behaviors (like sprinting and hopping) involving transient bursts of actuation coupled to the ground through internal elastic elements. The performance of such maneuvers is subject to reaction forces on the feet from the environment. On substrates like dry granular media, the laws that govern these forces are not fully understood, and can vary with foot size and shape, material compaction (measured by the volume fraction $\phi )$ and intrusion kinematics. To gain insight into how such interactions affect jumps on granular media, we study the performance of an actuated spring mass robot. We compare performance between two jump strategies: a single-cycle sine-wave actuation (a ``single jump'') and this actuation preceded by an impulsive preload (a ``preload jump''). We vary $\phi $ for both strategies, and find that $\phi $ significantly affects performance: we observe a 200{\%} increase in the single jump height with only a 5{\%} increase in volume fraction using a 7.62 cm diameter flat foot. The preload jump outperforms the single jump height by 150{\%} for all $\phi $. We hypothesize that this increase in performance results from higher intrusion velocities and accelerations associated with the preload. [Preview Abstract] |
Thursday, March 6, 2014 1:27PM - 1:39PM |
T1.00010: The effects of body properties on sand-swimming Sarah Sharpe, Robyn Kuckuk, Stephan Koehler, Daniel Goldman Numerous animals locomote effectively within sand, yet few studies have investigated how body properties and kinematics contribute to subsurface performance. We compare the movement strategies of two desert dwelling subsurface sand-swimmers exhibiting disparate body forms: the long-slender limbless shovel-nosed snake (\emph{C. occipitalis}) and the relatively shorter sandfish lizard (\emph{S. scincus}). Both animals ``swim'' subsurface using a head-to-tail propagating wave of body curvature. We use a previously developed granular resistive force theory to successfully predict locomotion of performance of both animals; the agreement with theory implies that both animal's swim within a self-generated frictional fluid. We use theory to show that the snake's shape (body length to body radius ratio), low friction and undulatory gait are close to optimal for sand-swimming. In contrast, we find that the sandfish's shape and higher friction are farther from optimal and prevent the sandfish from achieving the same performance as the shovel-nosed snake during sand-swimming. However, the sandfish's kinematics allows it to operate at the highest performance possible given its body properties. [Preview Abstract] |
Thursday, March 6, 2014 1:39PM - 1:51PM |
T1.00011: A scattering approach for locomotion on heterogeneous granular media Tingnan Zhang, Feifei Qian, Adam Kamor, Predrag Cvitanovic, Daniel Goldman Locomotion on homogeneous particulate media has been recently studied using biological and robotic experiment and modeled using multi-particle discrete element simulation and empirical resistive force theory. Little is known about how locomotion is affected when environments are composed of particles with a large distribution of sizes. We study in experiment and a reduced order model, locomotion dynamics when particle sizes are widely separated. A hexapedal robot ($\sim$15 cm, $\sim$100 g) interacts with a single boulder (whose size is comparable to the robot) during runs on a substrate of homogeneous, loosely packed poppy seeds. We vary the perpendicular distance between the center of the boulder and the trajectory of the robot's center of mass (CoM) before collision (the impact parameter), and measure the post-collision direction. For fixed impact parameter, the CoM deflection sensitively depends on the boulder contact point and leg phase. Counterintuitively, the interactions are largely attractive; the robot turns towards the scattering center. To understand the long-time dynamics, in a reduced-order model, we treat the scattering angle as a function of only the impact parameter with other effects modeled as noise; we thereby extend the study to an infinite field of boulders. [Preview Abstract] |
Thursday, March 6, 2014 1:51PM - 2:03PM |
T1.00012: Universality in legged locomotion on low-resistance ground Feifei Qian, Wyatt Korff, Paul Umbanhowar, Robert Full, Daniel Goldman Natural substrates like sand, snow, leaf litter and soil vary widely in penetration resistance, but little is known about how legged locomotors respond to this variation. To address this deficit, we built an air-fluidized trackway filled with granular material to control ground resistance. Resistance can be reduced to zero by increasing the upward flow of air through the bed. Using a hexapedal robot as our model locomotor, we systematically study how locomotion performance varies with penetration resistance, limb kinematics and foot morphology. A universal model, which combines robot kinematics and ground parameters, determines robot speed for all penetration resistances and captures the dependence of performance sensitivity on foot pressure and ground resistance. Expanding the scope of locomotors to include five organisms, we find that their performance on low-resistance ground is also well captured by the universal model. The model suggests that both increasing foot size and decreasing gait frequency reduce the performance loss as ground resistance decreases. Organisms may minimize the inertial effects of the granular media by maintaining maximum foot impact shear stresses through passive structures, e.g. long flexible toes, and active mechanisms, e.g. gait frequency control. [Preview Abstract] |
Thursday, March 6, 2014 2:03PM - 2:15PM |
T1.00013: Using a robot to study the evolution of legged locomotion Benjamin McInroe, Henry Astley, Daniel I. Goldman Throughout history, many organisms have used flipper-like limbs for both aquatic and terrestrial locomotion. Modern examples include mudskippers and sea turtles; extinct examples include walkers such as the early tetrapod\textit{ Ichthyostega}. In the transition from an aquatic to a terrestrial environment, early walkers had to adapt to the challenges of locomotion over flowable media like sand and mud. Previously, we discovered that a flipper with an elbow-like joint that could passively flex and extend toward and away from the body aided crawling on dry granular media [Mazouchova et. al. 2013], a result related to the jamming of material behind and beneath the flipper. To gain insight into how an additional degree of freedom of this joint affects flipper-based locomotors, we have built a robotic model with limb-joint morphology inspired by \textit{Ichthyostega}. We add to our previous limb design a passive degree of freedom that allows for supination/pronation of the flipper about a variable insertion angle. Springs at the joints restore the flippers to equilibrium positions after interaction with the media. We study the crutching locomotion of the robot performing a symmetric gait, varying flipper-joint degrees of freedom and limb cycle frequency. [Preview Abstract] |
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