Fall 2017 Schedule

DateSpeakerLab
8/31/17Perrin SchiebelGoldman lab
9/7/17Jianing WuHu Lab
9/14/17Yu-Hui LinWeitz group
9/21/17David Yanni
Yunker lab
9/28/17Bo Broadwater
Yasemin Ozkan Aydin
Kim lab
Goldman lab
10/5/17Izaak NevelnSponberg lab
10/12/17Claire Ji Fenton Lab
10/19/17Bahnisikha DuttaGoldman lab
10/26/17Sunny HwangGumbart lab
11/2/17Skanda VivekYunker lab
11/9/17Hector VelascoFenton lab
11/16/17Olga ShishkovHu Lab
11/23/17Thanksgiving Break
11/30/17Hemaa SelvakumarCurtis Lab

Fall 2017 Abstracts


08/31/2017

Perrin Schiebel

Collisional diffraction emerges from simple control in a sand-specialist snake

Elongate, limbless organisms such as snakes move through terrestrial terrains by propagating bends backward along the body. Previous research described how these bends are pressed against obstacles to propel the snake forward. However, we lack an understanding of the control mechanism which mediates the interaction between the snake and the surroundings. To discover principles of how and when to use obstacles, we studied a desert-dwelling snake, C. occipitalis, which uses a highly-stereotyped waveform to slither across homogeneous granular matter We tested the snake in a model terrestrial terrain—a single row of force-sensitive vertical posts embedded in a homogeneous substrate—and compared its performance with a robophysical model—a 12-link robotic snake using open-loop control to achieve a waveform similar to that used by C. occipitalis. We found the snake was more likely to apply force to the posts perpendicular to the direction of motion, meaning the snake was not utilizing the rigid posts to push itself forward. A similar pattern arose from the robot trials, suggesting that this may be an feature of open-loop control interacting with the obstacles. Furthermore, distributions of the snakes’ post-peg travel angles displayed preferred directions in a diffraction-like pattern with a central peak at zero and symmetric peaks at approximately plus and minus 20 and 40 degrees. This collisional diffraction pattern appeared in both the living and robot snake and persisted even when compliance was introduced to the robot’s control. This suggests that this sand-specialist snake adheres to its preferred waveform as opposed to changing the shape in response to the terrain. We posit that open-loop control of a stereotyped gait may be a simple strategy for movement in terrains with sparse heterogeneity, but if adherence to a heading is desired more sophisticated control is needed. 

09/07/2017

Jianing Wu

The elephant’s toolkit in the trunk: mechanical perfection and bio-inspired robotics

Elephant trunk is a muscular hydrostat which is comprised of 150,000 muscles, helping feed on 150 kg food every day. We found that, the elephant can grab items in a variety of sizes. For bran dust and smaller cubes, the elephant forms joint on the trunk to regulate jamming force when it grabs. For larger items, the elephant can grab aided by suction. Moreover, the elephant is able to grab heaviest items by wrapping the trunk and lifting with the elephant’s head, using the trunk as a lever. We fabricated a series of robots that not only demonstrate the strategies used for elephants’ grabbing, but open up new ways of designing universal grippers. 

09/14/2017

Yu-Hui Lin

The effects of spatial interactions on an oscillatory tragedy of the commons

Evolution game theory and replicator dynamics has been used as a theoretical frame work to study the temporal change of composition of a population. However, there is little consideration on the mutual feedback between individual behaviors and the abundance of common resources. Weitz et. al. (2016) proposed an ODE system coupling the dynamics of population composition and abundance of common resources, which demonstrates a tragedy of the commons. Following their work, we derived an individual-based model and extended it to include spatial dimensions and allow diffusion of common resources. When spatial dimension is in included, we found a tragedy of the commons will be averted in a wider range of parameter space if the spatial component is considered.

09/21/2017

David Yanni

Emergent multicellular traits are emergent physical phenomena in snowflake yeast

Multicellularity has developed multiple times in several lineages, but the profound transition our ancestors made from unicellularity happened over 600 million years ago, making it impossible to study in the lab. Snowflake yeast represents a model organism for the study of nascent multicellular life. Nascent multicellular organisms must develop heritable adaptions to group level selection in the absence of sophisticated developmental regulatory mechanisms. Here, we suggest that certain aspects of early multicellular regulation, such as the life cycle, may have emerged “for free” from physics, and propose an approach to describe such a process for snowflake yeast.

09/28/2017

Bo Broadwater

The Physics of DNA Strand Displacement