Dr Bin Cheng
Dr. Cheng was born and raised in China. He earned a Bachelor's degree in Mathematics from the Peking University (PKU) at Beijing, China in 2001, went on to study in the University of California at Los Angeles (UCLA), USA where he earned a Master's degree in Applied Mathematics in 2003, and in the University of Maryland, College Park (UMD), USA where he earned his Ph.D. in Applied Mathematics and Scientific Computing in 2007.
Dr. Cheng then took on a Hildebrandt Assistant Professorship (postdoctoral) at the University of Michigan, Ann Arbor, USA from 2007 to 2010, and a Research Assistant Professorship (postdoctoral) at the Arizona State University, Tempe, USA from 2010 to 2012.
Dr. Cheng joined the University of Surrey at Guildford, UK in January, 2013. He currently holds a Senior Lectureship (roughly the UK equivalent of tenured assistant professor) in the Department of Mathematics. His research interests sit in the general areas of applied mathematics and mathematical physics, especially in the analysis of nonlinear PDEs and applications to large-scale atmospheric and oceanic circulations. But he is curious just about everything.
Dr. Cheng has taught university-level mathematics for over 10 years, and has also delivered numerous seminars and colloquia. He has much experience in communicating mathematics to others and always enjoys doing so.
His personal website is at http://personal.maths.surrey.ac.uk/st/bc0012/
I am the PI of the project "Mathematical analysis of ‘near resonance’ in the physical world of finiteness" funded by a Leverhulme Research Project Grant (RPG-2017-098), 2017-2021.
I am also a co-I of the project "On the way to the asymptotic limit: mathematics of slow-fast coupling in PDEs" funded by an EPSRC Standard Research Grant (EP/R029628/1), 2018-2021.
Postgraduate research supervision
Despite many efforts in this direction, the IMs in the case when the spectral gap conditions are violated remain a mystery especially in the case of parabolic PDEs. On the one hand, there is a number of interesting classes of such equations where the existence of IMs is established without the validity of the spectral gap conditions and, on the other hand there were no examples of dissipative parabolic PDEs where the non-existence of an IM is rigorously proved.
The main aim of this thesis is to bring some light on this mystery by the comprehensive study of three model examples of parabolic PDEs where the spectral gap conditions are not satisfied, namely, 1D reaction-diffusion-advection (RDA) systems (see Chapter 3), the 3D Cahn-Hilliard equation on a torus (see Chapter 4) and the modified 3D Navier-Stokes equations (see Chapter 5). For all these examples the existence or non-existence of IM was an open problem.
As shown in Chapter 3, the existence or non-existence of an IM for RDA systems strongly depends on the boundary conditions. In the case of Dirichlet or Neumann boundary conditions, we have proved the existence of an IM using a specially designed non-local in space diffeomorphism which transforms the equations to the new ones for which the spectral gap conditions are satisfied. In contrast to this, in the case of periodic boundary conditions, we construct a natural example of a RDA system which does not possess an IM.
In Chapters 4 and 5 we develop an extension of the so-called spatial averaging principle (SAP) (which has been suggested by Sell and Mallet-Paret in order to treat scalar reaction-diffusion equation on a 3D torus) to the case of 4th order equations where the nonlinearity loses smoothness (the Cahn-Hilliard equation) as well as
problem is formulated in terms of conservation laws for mass, moist potential
temperature and specific humidity of air parcels. A numerical adjustment algorithm
is devised to model the convective adjustment of the column to a statically stable
equilibrium state for a number of test cases. The algorithm is shown to converge to
a weak solution with saturated and unsaturated parcels interleaved in the column as
the vertical spatial grid size decreases. Such weak solutions would not be obtainable via
discrete PDE methods, such as finite differences or finite volumes, from the governing
Eulerian PDEs. An equivalent variational formulation of the problem is presented and
numerical results show equivalence with those of the adjustment algorithm. Results are
also presented for numerical simulations of an ascending atmospheric column as a series
of steady states. The adjustment algorithm developed in this paper is advantageous
over similar algorithms because first it includes the latent heating of parcels due to
the condensation of water vapour, and secondly it is computationally efficient making it
implementable into current weather and climate models.
We state the conditions for it to represent a stable steady state. We then evolve
the column by subjecting it to an upward displacement which can release instability,
leading to a time dependent sequence of stable steady states. We propose a definition
of measure valued solution to describe the time dependence and prove its existence.
equations having two small parameters and hence three time scales are considered.
Under appropriate conditions solutions are shown to exist and remain uniformly
bounded for a fixed time as the two parameters tend to zero at different rates. A
simple example shows the necessity of those conditions in order for uniform bounds
to hold. Under further conditions the solutions of the original system tend to solutions
of a limit equation as the parameters tend to zero.
plays an important role in geophysical fluid dynamics. The main results contain two contrasting
aspects. First, when the solution crosses certain thresholds, we prove finite-time singularity
formation for the classical solutions by studying the weighted gradients of Riemann invariants
and utilizing conservation of physical energy. In fact, the singularity formation will take place for
a large class of
initial data whose gradients and physical energy can be arbitrarily small and
higher order derivatives should be large. Second, when the initial data have constant potential
vorticity, global existence of small classical solutions is established via studying an equivalent
form of a quasilinear Klein-Gordon equation satisfying certain null conditions. In this global
existence result, the smallness condition is in terms of the higher order Sobolev norms of the
will investigate, from the angle of partial differential equation
analysis, some oscillatory geophysical fluid dynamics in three
dimensions: Navier?Stokes equations in a fast-rotating, spherical shell, and magnetohydrodynamics subject to strong Coriolis
and Lorentz forces. Upon averaging their oscillatory solutions
in time, interesting patterns such as zonal flows can emerge.
More rigorously, we will prove that, when the restoring forces
are strong enough, time-averaged solutions stay close to the null
spaces of the wave operators, whereas the solutions themselves
can be arbitrarily far away from these subspaces.