September 21, 2018
Dr. Sookkyung Lim, UC Math
Conference room
Title: In silico flagellated micro-swimmers in a viscous fluid
Abstract: Swimming bacteria with helical flagella are self-propelled micro-swimmers in nature, and the swimming strategies of such bacteria vary depending on the number and the position of flagella on the cell body. In bacterial flagella-based propulsion, the major driving force comes from a rotary motor that is embedded in the cell body and is connected to the flagellar filament via a universal joint ‘hook.’ We will introduce two microorganisms, multi-flagellated E. coli and single-flagellated Vibrio A. The Kirchhoff rod theory is used to model the elastic helical flagellum together with the hook and the penalty method is employed to describe the dynamics of the rigid cell body. The hydrodynamic interaction between the fluid and the cell is represented by the regularized Stokes formulation. In this talk, we will focus on (1) how polymorphic transformation of the flagellum affects the dynamics of E. coli and (2) how hook’s buckling reorients swimming bacteria Vibrio A in new directions.
September 28, 2018
Wei Ning, Purdue U
Conference room
Title: The dual effect of ephaptic coupling on cardiac conduction with heterogeneous expression of connexin 43
Abstract: Decreased and heterogeneous expression of connexin 43 (Cx43) are common features in animal heart
failure models. Ephpatic coupling, which relies on the presence of junctional cleft space between the
ends of adjacent cells, has been suggested to play a more active role in mediating intercellular electrical
communication when gap junctions are reduced. To better understand the interplay of Cx43 expression
and ephaptic coupling on cardiac conduction during heart failure, we performed numerical simulations
on our model when Cx43 expression is reduced and heterogeneous. Under severely reduced Cx43
expression, we identified three new phenomena in the presence of ephaptic coupling: alternating
conduction, in which ephaptic and gap junction-mediated mechanisms alternate; instability of planar
fronts; and small amplitude action potential (SAP), which has a smaller potential amplitude than the
normal action potential. In the presence of heterogeneous Cx43 expression, ephaptic coupling can either
prevent or promote conduction block (CB) depending on the Cx43 knockout (Cx43KO) content. When
Cx43KO content is relatively high, ephaptic coupling reduces the probabilities of CB. However, ephaptic
coupling promotes CB when Cx43KO and wild type cells are mixed in roughly equal proportion, which
can be attributed to an increase in current-to-load mismatch.
October 5, 2018
None
October 12, 2018
Fall Break
October 19, 2018
Zhilan Feng, Purdue U
Conference room
Title:Plant toxins and trophic cascades alter fire regime and succession on a boreal forest
landscape
Abstract: Earlier models of plant-herbivore interactions relied on forms of functional response that
related rates of ingestion by herbivores to mechanical or physical attributes such as bite size
and rate. These models fail to predict a growing number of findings that implicate chemical
toxins as important determinants of plant-herbivore dynamics. Specifically, considerable
evidence suggests that toxins set upper limits on food intake for many species of herbivorous
vertebrates. Herbivores feeding on toxin-containing plants must avoid saturating their
detoxification systems, which often occurs before ingestion rates are limited by mechanical
handling of food items. We developed mathematical models with toxin-determined functional
responses to study the effects of inter-specific plant competition, herbivory, and a plant’s toxic
defenses against herbivores on vegetation dynamics. The new models exhibit much more
complex dynamics including Hopf and homoclinic bifurcations. We used the model to estimate
the effects of different levels of wolf control. Simulations indicated that management
reductions in wolf densities could reduce the mean time to transition from deciduous to spruce
by more than 10 years, thereby increasing landscape flammability. The integrated model can be
useful in estimating ecosystem impacts of wolf control and moose harvesting in central Alaska.
October 26, 2018
Tongli Zhang, Department of Pharmacology & Systems Physiology, UCCOM
Medical Campus
TBA
November 2, 2018
Chunhua shan, Toledo U
Conference room
TBA
November 9, 2018
Taige Wang, UC Math
Conference Room
TBA
November 16, 2018
Shaaban Abdallah, Dept. of Aerospace Eng., UC
Conference Room
TBA
November 23, 2018
Thanksgiving
November 29, 2018
(Thursday, 3:30pm)
David Sprinzak, Tel Aviv University
Medical Campus
TBA
November 30, 2018
None
December 7, 2018
Donald French, UC Math
Conference room
TBA