Dr Alexandra Tzella BA, DEA, PhD

Alexandra Tzella

School of Mathematics
Lecturer in Applied Mathematics

Contact details

Address
University of Birmingham
Edgbaston
Birmingham
B15 2TT
UK

Alexandra Tzella is a lecturer in Applied Mathematics. She is a member of the Continuum Mechanics and Nonlinear Systems research groups.  Alexandra's current research uses mathematical techniques to understand how tracers (e.g. pollutants) evolve in idealised fluid and porous media flows. A key challenge is to determine how structural inhomogeneities and physical and chemical processes impact on the long-time behaviour of the tracer concentrations.

Alexandra's work has focused on employing mathematical and computational methods to develop new models that provide better descriptions and efficient predictions of the concentrations in a number of idealised and environmental situations, with particular emphasis on environmental issues such as the distribution of plankton species in the ocean and contaminants in groundwater aquifers.

Qualifications

  • PhD in Applied Mathematics, University of Cambridge, 2008.
  • DEA (Masters) in Theoretical Physics, Université Paris VI, 2002.
  • BA (Hons) in Mathematics, University of Cambridge, 2000.

Biography

Alexandra Tzella studied at the University of Cambridge, UK, where she obtained a Bachelor's degree in Mathematics and at the Ecole Normale Supérieure (ENS) in Paris, France where she obtained a Master’s degree in Theoretical Physics.  She went on to complete a PhD in fluid dynamics under the supervision of Prof. Peter H. Haynes at the Department of Applied Mathematics and Theoretical Physics, University of Cambridge, UK. 

Alexandra was awarded Marie-Curie and ENS fellowships to undertake research at the Laboratoire de Météorologie Dynamique at ENS in Paris, working with Drs Bernard Legras and Fabio Andrea which gave her invaluable experience in atmospheric research. She returned to the UK to take up a post-doctoral position at the University of Edinburgh working with Prof. Jacques Vanneste on fundamental aspects of mixing before starting her current position at the University of Birmingham. 

Research

Research themes

Transport & mixing

Large-scale random flows. The distribution of atmospheric greenhouse gases and oceanic plankton species in the ocean are characterised by fine-scale, strongly inhomogeneous, complex structures that characterise the corresponding tracer fields. These structures are beautiful and striking physical phenomena; they can also have a large-scale impact on the climate of our planet. Alexandra’s research has focused on employing analytical and numerical methods (dynamical systems, analytical bounds, stochastic and data-driven Lagrangian modelling) to obtain reduced descriptions that yield predictions, in a number of idealised and environmental situations where the underlying flow is predominantly large-scale and random. 

Past collaborations: Prof. Peter H. Haynes (University of Cambridge), Dr Bernard Legras (ENS, Paris).

Porous media. Structural inhomogeneities in porous media can strongly impact on the transport of constituents evolving therein. Using the theory of large deviations together with multiscale and matched asymptotics, Alexandra’s research has developed a new range of simplified models that capture the evolution of the constituent concentration after long times, when the spatial scale of the concentration fields is much larger than that of the medium. Explicit results provide new insight into the way media with complex network geometries and obstacles affect the distribution of low scalar concentrations where classical predictions (obtained via the method of homogenisation) fail. 

Current collaborations: Yahya Farah (EPSRC funded PhD student), Dr Daniel Loghin (University of Birmingham), Prof. Jacques Vanneste (University of Edinburgh). 

Reactive front propagation

Cut-off reactions. Reactive fronts arise in a wide range of applications in mathematical chemistry and biology. They describe the spatial invasion of chemical or biological reactions and are usually established as a result of the interaction between molecular diffusion, local growth, and saturation. Their propagation can be strongly affected by a reaction that is effectively deactivated at points where the concentration lies below a threshold cut-off value. Such reactions are motivated by applications in combustion or systems of interacting particles in which case the cut-off value may be viewed as the effective mass of a single particle. Using a combination of classical analysis and asymptotic methods, Alexandra's research determines the long-time behaviour of the reactive front and approximates it in the limit of small and large cut-off values. 

Current collaborations: Prof. Dave Needham (University of Birmingham),  Dr Alex D. O. Tisbury (EPSRC funded PhD student).

Periodic flows. In a wide range of environmental systems and engineering applications, the propagation of reactive fronts can be greatly facilitated by advection which typically increases the effective area of the reaction. A new range of simplified models developed in Alexandra's research explain the role of stagnation points in slowing down the propagation of fronts, elucidate differences between alternative models of reaction and determine their impact in a variety of periodic flows. 

Current collaborations: Prof. Dave Needham (University of Birmingham), Prof. Jacques Vanneste (University of Edinburgh). 

Publications

A full list of papers can be found in Google Scholar.

View all publications in research portal