Exposés de recherche par les étudiants gradués
Org:
Irena Papst et
Adrien Thierry (McMaster)
[
PDF]
 ZAFER SELCUK AYGIN, Carleton University
Fourier series representations of new classes of eta quotients [PDF]

The Dedekind eta function $\eta (z)$ is the holomorphic function defined on the upper half plane $ \{ z \in \mathbb{C} \mid \mbox{ Im}(z) >0 \}$
by the product formula
\begin{equation*}
\eta (z) = e^{\pi i z/12} \prod_{n=1}^{\infty} (1e^{2\pi inz}).
\end{equation*}
We determine Fourier series representations of new classes of etaquotients of weight $2$. For example we show that
\begin{equation*}
\frac{\eta^{3}(2z)\eta(4z)\eta^{2}(8z)}{\eta^{2}(z)} = \sum_{n=1}^{\infty} \Big( \sum_{mn} \Bigl({\frac{8}{m}}\Bigr) m \Big) e^{2\pi i nz},
\end{equation*}
where $\Bigl({\frac{8}{m}}\Bigr) $ is the KroneckerJacobi symbol.
We prove our results using the theory of modular forms. This is a joint work with Ayse Alaca and Saban Alaca
 ALI GHASEMI, McMaster University
Simulation of high Reynolds fluid flow through an array of moving cylinders [PDF]

Because of its practical importance in industrial applications, many
attempts have been made to understand the instability of flowinduced
vibration of a periodic array of elastically mounted cylinders. It
has been suggested that the instability depends on parameters such as
geometry, mass damping and natural frequency of the array as well as
the mean velocity of the cross flow. Unfortunately, the available
experimental provide conflicting evidence for the stabilizing or
destabilizing role of the flow's Reynolds number and turbulence
intensity. In order to investigate this problem, we are using a high
resolution pseudospectral scheme to solve the NavierStocks equations
and Brinkman volume penalization to impose noslip boundary conditions
on the surfaces of the moving cylinders. Our goal is to vary the
turbulence intensity, Reynolds number and mean velocity to better
understand the role of turbulence in fluidelastic instability. In
this presentation I will focus on my initial work developing numerical
tools to efficiently simulate the flow on large numbers of processors.
 SPENCER HUNT, McMaster University
HPV Type Replacement and Spatial WithinHost Modelling [PDF]

The human papillomavirus (HPV) is a ubiquitous, multitype virus that affects many Canadians. Most infections with HPV are transient and cleared by the body naturally. However, persistent infection may lead to precancerous and cancerous lesions. Vaccines against two cancerous types (HPV16 and 18) have been developed recently. However, researchers are concerned about the possibility of type replacement occurring. This is a phenomenon wherein the vaccination against certain vaccine types of a pathogen causes the niche space for nonvaccine types to be expanded due to the decreased prevalence of these vaccine types. This can result in the increased prevalence of other cancerous nonvaccine HPV types, which may lessen the benefits of the vaccine. Previous mathematical models have been used to examine the potential for type replacement occurring. These models show that HPV type replacement hinges on HPV type interactions. Spatial withinhost models can be used to examine HPV types interactions in more detail. This can give researchers and epidemiologists more insight into the potential for HPV type replacement and its implications.\
In this talk, I will quickly review some ecological considerations that must be made when developing spatial withinhost models for HPV. I will then showcase a spatial model, outlining the important mechanisms of the model. I will wrap up by discussing some analytical results of the model.
 SERGEI MELKOUMIAN, McMaster University
The Effects of Wakes and Multiple Moving Bodies on Darwinian Drift [PDF]

When a body passes through an unbounded fluid, it induces a net
displacement of fluid particles. The difference between the initial
and final positions of a fluid particle is defined as the particle’s
Darwinian ``drift'', and plays an important role in the characterization
of the stirring occurring in multiphase flows and due to swimming
bodies. For instance, there is evidence to suggest that the drift due
to swimming bodies such as zooplankton or larger mammals in the oceans is
a significant contributor to overall ocean circulation and nutrient
transport. In this talk, we will discuss the effect of vortex wakes
on the Lagrangian displacement of particles induced by the passage of an
obstacle in a twodimensional incompressible and inviscid fluid. Further,
we will discuss the ongoing work concerning the drift induced
by pairs or larger groups of moving obstacles where such flows can be
studied using the formalism based on the SchottkyKlein prime function.
 ATHINTHRA SETHURAJAN, McMaster University
Reconstruction of StateDependant Material Properties and Its Application in Electrochemical Systems [PDF]

Outlining a computational approach to the solution of an inverse modelling problem concerning the material properties of electrolytes used in Lithiumion batteries is the main theme of this presentation. The dependence of material properties on the concentration of Lithium ions is reconstructed based on the concentration data obtained from an insitu NMR imaging experiment. This experiment is modelled by a 1D timedependent PDE describing the evolution of the concentration of Lithium ions with prescribed initial concentration and fluxes at the boundary. The material properties that appear in this model are reconstructed by solving a variational optimization problem in which the leastsquare error between the experimental and simulated concentration values is minimized. This optimization problem is solved using an innovative gradientbased method in which the gradients are obtained with adjoint analysis. Steps to obtain gradients through adjoint analysis, validational studies on the computational framework for this reconstruction problem and reconstructed material properties of a labmanufactured and a commercial battery electrolyte are presented with insights which complement available experimental results.
 YUSUKE SHIMABUKURO, McMaster University
Nonlinear waves in the integrable systems [PDF]

Wave phenomena occur everywhere in our surroundings, as for instance in water, acoustic, electromagnetic, and quantum waves, and so on, which have been modeled by nonlinear partial differential equations. Among a plethora of solutions in such equations, a localized and smooth wave retaining its shape, speed, and amplitude is often referred as a soliton. We will present orbital stability of a soliton in the integrable system on a class of nonlinear Dirac equations. This is a joint work with Dmitry Pelinovsky and Andres Contreras.
 PETER SINCLAIR, McMaster University
Computable Axiomatizability of Elementary Classes [PDF]

Determining whether a class of modeltheoretic structures has a computable axiomatization is a straightforward question which can have surprising answers. The class of all fields, for example, is easily axiomatized, as is the class of fields of characteristic zero; however, the class of all fields of nonzero characteristic is not.
A more complicated example is the class consisting of ultraproducts of ominimal structures (definitions of these terms will be given during the presentation). Multiple proposals were made for possible axiomatizations of this class, but Alex Rennet showed in a recent paper that in any proper expansion of the ordered ring language, this class is not axiomatizable. I will present a generalized version of Rennet's theorem, along with examples of classes that the theorem can be applied to.
 ADRIEN THIERRY, McMaster
Inversion factor. [PDF]

In combinatorics on words, counting the different types of squares is a fundamental problem. It was well understood that at most two different squares could have their last occurrence starting at the same position, but little was known about them. The recent advance in the field relies on the combinatorial structures of those doublesquares. We will take a look here at those structures, and a particularly important one: the inversion factor, and see how they can lead to a better bound for the maximal number of distinct squares in a string.
© Société mathématique du Canada