OttovonGuericke University Magdeburg, Germany

Tue 1 Apr 2014, 12:30pm
Scientific Computation and Applied & Industrial Mathematics
ESB 4133

Preconditioning for vectorvalued CahnHilliard equations

ESB 4133
Tue 1 Apr 2014, 12:30pm2:00pm
Abstract
The solution of vectorvalued Cahn–Hilliard systems is of interest in many applications. We discuss strategies for the handling of smooth and nonsmooth potentials as well as for different types of constant mobilities. Whereas the use of smooth potentials leads to a system of parabolic partial differential equalities, the nonsmooth ones result in variational inequalities. Concerning the latter, we propose a Moreau–Yosida regularization technique that incorporates the necessary bound constraints. As a result, the variational inequalities are replaced by nonsmooth equations. Due to the use of fully implicit time discretizations, which are the most accurate, we have to solve in every time step nonlinear smooth or nonsmooth equations. This is done by standard Newton methods in the smooth case, and by semismooth Newton methods in the nonsmooth case. At the heart of both methods lies the solution of large and sparse linear systems for which we propose the use of preconditioned Krylov subspace solvers using an effective Schur complement approximation. Numerical results illustrate the efficiency of our approach. In particular, we numerically show mesh and phase independence of the developed preconditioner in the smooth case. The results in the nonsmooth case are also satisfying and the preconditioned version always outperforms the unpreconditioned one. (Joint work with Martin Stoll.)
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University of Warwick

Wed 2 Apr 2014, 3:00pm
Probability Seminar
ESB 2012

Gibbs formalism for Random Permutations

ESB 2012
Wed 2 Apr 2014, 3:00pm4:00pm
Abstract
We will introduce a whole range of problems related to random permutations whose motivation goes back to the BoseEinstein condensation in quantum statistical mechanics. After reviewing standard probabilistic approaches we will introduce a Gibbs formalism for random bijections of the planar integer lattice. Under certain energy assumptions we show the existence of Gibbs measures and discuss possible characterisation of different phases and address the problem of finite and infinite cycles in bijections of the planar integer lattice.
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Ph.D. Candidate, EPFL, Switzerland

Wed 2 Apr 2014, 3:00pm
Fluids Lab Meeting
LSK 203

NUMERICAL SIMULATIONS OF KATABATIC FLOWS

LSK 203
Wed 2 Apr 2014, 3:00pm4:00pm
Abstract
From the standpoint of basic fluid dynamics, katabatic winds are buoyantly driven boundarylayertype flows along heated or cooled sloping surfaces in a stratified fluid. However, understanding their structure is of interest not only as a fundamental problem in itself, but also from a meteorological point of view, because of the broad range of areas and scales that they cover, influencing from local valleys microclimate (e.g. over Salt Lake and Phoenix valleys) to synoptic scale motions (e.g. over ice sheets in coastal regions in Antarctica).
In katabatic flows turbulence is generated by shear and destroyed by negative buoyancy and viscosity. Because of this interplay between shear and buoyancy effects the strength of turbulence in the stable boundary layer that arise is much weaker, in comparison to the neutral and convective boundary layers, and this feature, together with the intrinsic complex dynamics of the system (e.g. occurrences of intermittency, KelvinHelmholtz instability, gravity waves, lowlevel jets and meandering motions) and the lack of any similarity theory, pose heavy burdens on numerical simulations.
The presentation will provide a brief overview of the stateoftheart in numerical modeling of slope flows to then focus on recent numerical analyses, under idealized settings, which somehow resemble Prandtl's original model (1942)  an early milestone in the conceptual understanding of slope flows.
A modified set of filtered Boussinesq equations are solved on a regular domain relying on an operatorsplitting technique to decouple the system. A mixed pseudospectral and finite difference approach is adopted in space and the fully explicit secondorder accurate AdamsBashforth scheme is used for time advancement. Closure of the equations is achieved through first order algebraic Smagorinsky models.
A statistical analysis of the initial oscillatory transient and on the properties of the steady state solution will be presented for a given subset of the parameter space, followed by an eduction of the coherent structures populating the flow. The behavior of Smagorinskytype subgridscale models for such systems will also be discussed.
Here is a little intro about Marco:
 2008 > B.A. in Civil Engineering (University of Padua  Italy)
 2010 > M.A. in Civil Engineering (University of Padua  Italy), Thesis at the International Center for Numerical Methods in Engineering (CIMNE), Barcelona
 2012 > PhD candidate in Mechanical Engineering at École Polytechnique Fédérale de Lausanne (EPFL), at the EFLUM Lab. (Environmental Fluid Mechanics).
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McMaster University

Wed 2 Apr 2014, 3:15pm
Topology and related seminars
ESB 4133

Finite group actions and chain complexes over the orbit category

ESB 4133
Wed 2 Apr 2014, 3:15pm4:15pm
Abstract
The unit spheres in orthogonal representations of finite groups give examples of group actions on spheres. We investigate nonlinear actions by studying chain complexes over the orbit category, and constructing finite GCW complexes. This leads to new examples of homotopy representations with isotropy of rank one. This project is joint with Ergun Yalcin (Bilkent University, Ankara).
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PIMS/University of Calgary

Thu 3 Apr 2014, 3:30pm
Number Theory Seminar
room MATH 126

The Greenberg transform in the representation theory of padic groups

room MATH 126
Thu 3 Apr 2014, 3:30pm4:30pm
Abstract
The standard framework for studying representation theory of padic Lie groups is that of reductive groups over a padic field K. In this talk I will describe ongoing work with Clifton Cunningham and Takashi Suzuki where we instead work with limits of group schemes over the residue field of K. In particular, I will describe a sheaffunction dictionary for quasicharacters of tori over local fields, and early progress toward a definition for the affine Grassmannian for reductive groups over K.
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UBC

Thu 3 Apr 2014, 4:00pm
Symbolic Dynamics and Ergodic Theory Seminar
Math Annex 1102

Phase Transitions and Computational Complexity (VI)

Math Annex 1102
Thu 3 Apr 2014, 4:00pm5:30pm
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Rutgers, Newark

Fri 4 Apr 2014, 2:00pm
CRG Geometry and Physics Seminar
ESB 4127 (host: UAlberta)

Stability and compactification of moduli

ESB 4127 (host: UAlberta)
Fri 4 Apr 2014, 2:00pm3:00pm
Abstract
In order to construct the moduli space of canonical polarized manifolds, three different stability conditions have been introduced, namely, KSBAstability, Kstabilty and asymptotic GIT stability. In this talk, we try to explore the relations among them. In particular, any canonical polarized manifold is stable with respect to all three conditions above, however the compactifications they give are different. As a consequence, we answer a longstanding question by showing that asymptotically GIT Chow semistable varieties do not form a proper family.
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UBC

Fri 4 Apr 2014, 3:00pm
Graduate Student Seminar
MATX 1100

Quantum unique ergodicity and related things

MATX 1100
Fri 4 Apr 2014, 3:00pm4:30pm
Abstract
We will first describe the conjecture of 'Quantum Unique Ergodicity' which is also known as 'Quantum Chaos'. This problem is in the intersection of Dynamical Systems, Harmonic Analysis, PDE, Differential Geometry and Mathematical Physics, and therefore attracts almost all branches of mathematics. Secondly, we will see why number theorists got immensely interested in this problem which is apparently coming from a different field of mathematics. We will also give a brief description of Lindenstrauss' groundbreaking work on this problem in a special case, for which he got Fields Medal in the ICM 2010.
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UBC

Fri 4 Apr 2014, 3:00pm
Graduate Student Seminar
MATX 1100

Model Theory

MATX 1100
Fri 4 Apr 2014, 3:00pm4:30pm
Abstract
We will introduce the basic notions of first order model theory, the
study of first order theories and their structures. Many familiar
classes of mathematical objects are first order theories, such as
groups, fields, ZFC, some theories of arithmetic, and more. I will
present some basic theorems and present an interesting result, Skolem's
Paradox.
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PIMS/UBC

Mon 7 Apr 2014, 1:50pm
CRG Geometry and Physics Seminar
ESB 4127 (host: UBC)

Special reductive groups over an arbitrary field

ESB 4127 (host: UBC)
Mon 7 Apr 2014, 1:50pm2:50pm
Abstract
A linear algebraic group G defined over a field k is called special if every Gtorsor over every field extension of k is trivial. In a modern language, it can be shown that the special groups are those of essential dimension zero. In 1958 Grothendieck classified special groups in the case where the base field k is algebraically closed. In this talk I will explain some recent progress towards the classification of special reductive groups over an arbitrary field. In particular, I will give the classification of special semisimple groups, special reductive groups of inner type and special quasisplit reductive groups over an arbitrary field k.
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McGill

Mon 7 Apr 2014, 3:00pm
SPECIAL
Department Colloquium
ESB 2012 (PIMS building)

General Relativity, differential geometry and differential equations; stories from a successful menageatrois. (CRM Fields PIMS prize lecture)

ESB 2012 (PIMS building)
Mon 7 Apr 2014, 3:00pm4:00pm
Abstract
It is well known that Einstein's general theory of relativity provides a geometrical description of gravity in terms of spacetime curvature. Einstein's theory poses some fascinating and difficult mathematical challenges that have stimulated a great deal of research in geometry and partial differential equations. Important questions include the wellposedness of the evolution problem, the definition of mass and angular momentum, the formation of black holes, the cosmic censorship hypothesis, the linear and nonlinear stability of black holes and boundary value problems at conformal infinity arising in the analysis of the AdS/CFT correspondence. I will give a nontechnical survey of some
significant advances and open problems pertaining to a number of these questions.
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UBC

Wed 9 Apr 2014, 12:30pm
SPECIAL
Graduate Student Centre, room 203

Essential Dimension and Linear Codes

Graduate Student Centre, room 203
Wed 9 Apr 2014, 12:30pm2:00pm
Details
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University of Victoria

Wed 9 Apr 2014, 3:15pm
SPECIAL
Topology and related seminars
ESB 2012

Triangulations of 4manifolds and a table of knots in homotopy 4spheres

ESB 2012
Wed 9 Apr 2014, 3:15pm4:15pm
Abstract
I will describe a project to classify all smooth 4dimensional manifolds triangulable with 6 or less 4dimensional simplices. In the process we have found many simple triangulated 2knot exteriors, forming a strong analogy with 3manifold theory.
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PhD Candidate, Department of Meteorology, The Pennsylvania State University

Wed 9 Apr 2014, 4:00pm
Fluids Lab Meeting
LSK 203

Turbulent transport and convective organization in the unstable atmospheric boundary layer

LSK 203
Wed 9 Apr 2014, 4:00pm5:00pm
Abstract
The traditional framework in the atmospheric boundary layer for relating turbulent fluxes of momentum, heat, and scalar quantities to their mean gradients, called MoninObukhov similarity theory (MOST) after its originators, can be viewed as an extension of law of the wall scaling to account for the effects of thermal stratification. Although MOST is the standard framework for interpreting atmospheric measurements and modeling turbulent fluxes in weather and climate models, a number of fundamental issues in MOST still are not well understood. Because MOST arises from dimensional analysis, the connections between the curves that relate turbulent fluxes to mean gradients and fundamental properties of turbulence (e.g. the spectra, integral scales, and TKE budget) are not well understood. Furthermore, although experimental data often indicate deviations from MOST, the cause of these deviations (experimental error vs. physical processes) remains an open question.
In this presentation, a theoretical framework to connect MOST curves to fundamental properties of turbulence will be introduced. Experimental data will be used to demonstrate the effects of buoyancy on the integral length scales and their linkage to the behavior of MOST curves. Asymptotic solutions for MOST curves will also be derived for slightly unstable and free convective conditions.
In the second part of the talk, error propagation analysis and atmospheric data will be used to quantify the extent to which deviations from MOST are due to experimental errors vs. physical processes that are not represented by MOST. Deviations from MOST are found to have a strong diurnal trend, which suggest that processes related to the growth of the unstable atmospheric boundary layer remain unaccounted for in MOST.
The final part of the talk will focus on the how buoyancy and mean shear together influence the largescale organization of the unstable atmospheric boundary layer. For slightly unstable conditions, convective updrafts organize into longitudinal rolls, aligned with the mean wind; for highly convective conditions, updrafts organize into cells, similar to RayleighBenard convection. Using large eddy simulation, the transition from roll to cellular type convection will be examined. A transitional state between rolls and cells is observed and is characterized by oscillatory behavior in velocity statistics and convective organization. The physical processes responsible for this transition will be discussed.
Bio statement written by Scott: "I received my B.S. in Science Education from Martin Luther College in New Ulm, MN in 2008. In 2010, I received my M.S. in Meteorology from Penn State University. I will complete my Ph.D. (also in Meteorology) from Penn State University in May 2014, working with Prof. Marcelo Chamecki. My research interests include turbulence, the atmospheric boundary layer, and environmental fluid mechanics"
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UBC

Thu 10 Apr 2014, 4:00pm
Symbolic Dynamics and Ergodic Theory Seminar
Math Annex 1102

Phase Transitions and Computational Complexity (VII) CANCELLED

Math Annex 1102
Thu 10 Apr 2014, 4:00pm5:30pm
Abstract
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Mon 14 Apr 2014, 9:00am
SPECIAL
Graduate Student Center, Room 203

Doctoral Exam

Graduate Student Center, Room 203
Mon 14 Apr 2014, 9:00am11:00am
Details
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Mon 14 Apr 2014, 12:30pm
SPECIAL
Graduate Student Center, Room 203

Doctoral Exam

Graduate Student Center, Room 203
Mon 14 Apr 2014, 12:30pm2:30pm
Details
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Yale University.

Mon 14 Apr 2014, 4:00pm
SPECIAL
Department Colloquium
MATX 1100

Rightangled Artin groups, braid groups, diffeomorphism groups, and hyperbolic manifolds

MATX 1100
Mon 14 Apr 2014, 4:00pm5:00pm
Abstract
I will discuss some recent developments in hyperbolic geometry and geometric group theory, namely Agol's proof of the virtual Haken conjecture and Wise's theory of special groups, together with their relationship with rightangled Artin groups and mapping class groups. I will then discuss a new result which shows that every hyperbolic 3manifold admits a finite cover whose fundamental group embeds into a braid group, and into the group of diffeomorphisms of the circle. Finally, I will exhibit some higher dimensional closed hyperbolic manifold subgroups of braid groups and of the diffeomorphism group of the circle. The research in this talk represents work joint with Hyungryul Baik and Sanghyun Kim.
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Alex Tomberg and the Math Learning Centre Committee
Mathematics, UBC

Tue 15 Apr 2014, 2:00pm
SPECIAL
MATH 126

MLC EndofTerm Meeting

MATH 126
Tue 15 Apr 2014, 2:00pm4:00pm
Details
We will discuss the operations of the MLC this term, including attendance statistics and feedback from students and TAs. All are welcome to attend.
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Yale University

Tue 15 Apr 2014, 3:15pm
SPECIAL
Topology and related seminars
ESB 4133

Antitrees and rightangled Artin subgroups of planar braid groups

ESB 4133
Tue 15 Apr 2014, 3:15pm4:15pm
Abstract
We discuss a result which shows that every rightangled Artin group quasiisometrically embeds in a planar pure braid group. As a consequence, we obtain examples of quasiisometrically embedded closed hyperbolic manifold subgroups of pure braid groups in all dimensions. We also give some applications to decision problems in braid group theory. This represents joint work with Sanghyun Kim.
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University of Warwick

Tue 15 Apr 2014, 3:30pm
Diff. Geom, Math. Phys., PDE Seminar
ESB 2012

Directional oscillations, concentrations, and compensated compactness via microlocal compactness forms

ESB 2012
Tue 15 Apr 2014, 3:30pm4:30pm
Abstract
Microlocal compactness forms (MCFs) are a new tool to study oscillations and concentrations in L^pbounded sequences of functions. Decisively, MCFs retain information about the location, value distribution, and direction of oscillations and concentrations, thus extending both the theory of (generalized) Young measures and the theory of Hmeasures. Since in L^pspaces oscillations and concentrations precisely discriminate between weak and strong compactness, MCFs allow to quantify the difference between these two notions of compactness. The definition involves a Fourier variable, whereby also differential constraints on the functions in the sequence can be investigated easily. Furthermore, pointwise restrictions are reflected in the MCF as well, paving the way for applications to Tartar's framework of compensated compactness; consequently, we establish a new weaktostrong compactness theorem in a "geometric" way. Moreover, the hierarchy of oscillations with regard to slow and fast scales can be investigated as well since this information is also is reflected in the generated MCF.
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UBC

Thu 24 Apr 2014, 4:00pm
Symbolic Dynamics and Ergodic Theory Seminar
Math Annex 1102

Computing entropy and pressure of stationary Z^d Markov random fields

Math Annex 1102
Thu 24 Apr 2014, 4:00pm5:30pm
Abstract
For any stationary mZ^d Gibbs measure that satisfies strong spatial mixing, we obtain sequences of upper and lower approximations that converge to its entropy. In the case d=2, these approximations are efficient in the sense that they are accurate to within epsilon and can be computed in time polynomial in 1/epsilon. The method is extended to approximate pressure of Gibbs interactions. Joint work with Ronnie Pavlov.
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Note for Attendees
Notice the special time and place. Last seminar of the academic year. Sushi will be served.