Project acronym 3DWATERWAVES
Project Mathematical aspects of three-dimensional water waves with vorticity
Researcher (PI) Erik Torsten Wahlén
Host Institution (HI) LUNDS UNIVERSITET
Call Details Starting Grant (StG), PE1, ERC-2015-STG
Summary The goal of this project is to develop a mathematical theory for steady three-dimensional water waves with vorticity. The mathematical model consists of the incompressible Euler equations with a free surface, and vorticity is important for modelling the interaction of surface waves with non-uniform currents. In the two-dimensional case, there has been a lot of progress on water waves with vorticity in the last decade. This progress has mainly been based on the stream function formulation, in which the problem is reformulated as a nonlinear elliptic free boundary problem. An analogue of this formulation is not available in three dimensions, and the theory has therefore so far been restricted to irrotational flow. In this project we seek to go beyond this restriction using two different approaches. In the first approach we will adapt methods which have been used to construct three-dimensional ideal flows with vorticity in domains with a fixed boundary to the free boundary context (for example Beltrami flows). In the second approach we will develop methods which are new even in the case of a fixed boundary, by performing a detailed study of the structure of the equations close to a given shear flow using ideas from infinite-dimensional bifurcation theory. This involves handling infinitely many resonances.
Summary
The goal of this project is to develop a mathematical theory for steady three-dimensional water waves with vorticity. The mathematical model consists of the incompressible Euler equations with a free surface, and vorticity is important for modelling the interaction of surface waves with non-uniform currents. In the two-dimensional case, there has been a lot of progress on water waves with vorticity in the last decade. This progress has mainly been based on the stream function formulation, in which the problem is reformulated as a nonlinear elliptic free boundary problem. An analogue of this formulation is not available in three dimensions, and the theory has therefore so far been restricted to irrotational flow. In this project we seek to go beyond this restriction using two different approaches. In the first approach we will adapt methods which have been used to construct three-dimensional ideal flows with vorticity in domains with a fixed boundary to the free boundary context (for example Beltrami flows). In the second approach we will develop methods which are new even in the case of a fixed boundary, by performing a detailed study of the structure of the equations close to a given shear flow using ideas from infinite-dimensional bifurcation theory. This involves handling infinitely many resonances.
Max ERC Funding
1 203 627 €
Duration
Start date: 2016-03-01, End date: 2021-02-28
Project acronym AFRODITE
Project Advanced Fluid Research On Drag reduction In Turbulence Experiments
Researcher (PI) Jens Henrik Mikael Fransson
Host Institution (HI) KUNGLIGA TEKNISKA HOEGSKOLAN
Call Details Starting Grant (StG), PE8, ERC-2010-StG_20091028
Summary A hot topic in today's debate on global warming is drag reduction in aeronautics. The most beneficial concept for drag reduction is to maintain the major portion of the airfoil laminar. Estimations show that the potential drag reduction can be as much as 15%, which would give a significant reduction of NOx and CO emissions in the atmosphere considering that the number of aircraft take offs, only in the EU, is over 19 million per year. An important element for successful flow control, which can lead to a reduced aerodynamic drag, is enhanced physical understanding of the transition to turbulence process.
In previous wind tunnel measurements we have shown that roughness elements can be used to sensibly delay transition to turbulence. The result is revolutionary, since the common belief has been that surface roughness causes earlier transition and in turn increases the drag, and is a proof of concept of the passive control method per se. The beauty with a passive control technique is that no external energy has to be added to the flow system in order to perform the control, instead one uses the existing energy in the flow.
In this project proposal, AFRODITE, we will take this passive control method to the next level by making it twofold, more persistent and more robust. Transition prevention is the goal rather than transition delay and the method will be extended to simultaneously control separation, which is another unwanted flow phenomenon especially during airplane take offs. AFRODITE will be a catalyst for innovative research, which will lead to a cleaner sky.
Summary
A hot topic in today's debate on global warming is drag reduction in aeronautics. The most beneficial concept for drag reduction is to maintain the major portion of the airfoil laminar. Estimations show that the potential drag reduction can be as much as 15%, which would give a significant reduction of NOx and CO emissions in the atmosphere considering that the number of aircraft take offs, only in the EU, is over 19 million per year. An important element for successful flow control, which can lead to a reduced aerodynamic drag, is enhanced physical understanding of the transition to turbulence process.
In previous wind tunnel measurements we have shown that roughness elements can be used to sensibly delay transition to turbulence. The result is revolutionary, since the common belief has been that surface roughness causes earlier transition and in turn increases the drag, and is a proof of concept of the passive control method per se. The beauty with a passive control technique is that no external energy has to be added to the flow system in order to perform the control, instead one uses the existing energy in the flow.
In this project proposal, AFRODITE, we will take this passive control method to the next level by making it twofold, more persistent and more robust. Transition prevention is the goal rather than transition delay and the method will be extended to simultaneously control separation, which is another unwanted flow phenomenon especially during airplane take offs. AFRODITE will be a catalyst for innovative research, which will lead to a cleaner sky.
Max ERC Funding
1 418 399 €
Duration
Start date: 2010-11-01, End date: 2015-10-31
Project acronym BOPNIE
Project Boundary value problems for nonlinear integrable equations
Researcher (PI) Jonatan Carl Anders Lenells
Host Institution (HI) KUNGLIGA TEKNISKA HOEGSKOLAN
Call Details Consolidator Grant (CoG), PE1, ERC-2015-CoG
Summary The purpose of this project is to develop new methods for solving boundary value problems (BVPs) for nonlinear integrable partial differential equations (PDEs). Integrable PDEs can be analyzed by means of the Inverse Scattering Transform, whose introduction was one of the most important developments in the theory of nonlinear PDEs in the 20th century. Until the 1990s the inverse scattering methodology was pursued almost entirely for pure initial-value problems. However, in many laboratory and field situations, the solution is generated by what corresponds to the imposition of boundary conditions rather than initial conditions. Thus, an understanding of BVPs is crucial.
In an exciting sequence of events taking place in the last two decades, new tools have become available to deal with BVPs for integrable PDEs. Although some important issues have already been resolved, several major problems remain open.
The aim of this project is to solve a number of these open problems and to find solutions of BVPs which were heretofore not solvable. More precisely, the proposal has eight objectives:
1. Develop methods for solving problems with time-periodic boundary conditions.
2. Answer some long-standing open questions raised by series of wave-tank experiments 35 years ago.
3. Develop a new approach for the study of space-periodic solutions.
4. Develop new approaches for the analysis of BVPs for equations with 3 x 3-matrix Lax pairs.
5. Derive new asymptotic formulas by using a nonlinear version of the steepest descent method.
6. Construct disk and disk/black-hole solutions of the stationary axisymmetric Einstein equations.
7. Solve a BVP in Einstein's theory of relativity describing two colliding gravitational waves.
8. Extend the above methods to BVPs in higher dimensions.
Summary
The purpose of this project is to develop new methods for solving boundary value problems (BVPs) for nonlinear integrable partial differential equations (PDEs). Integrable PDEs can be analyzed by means of the Inverse Scattering Transform, whose introduction was one of the most important developments in the theory of nonlinear PDEs in the 20th century. Until the 1990s the inverse scattering methodology was pursued almost entirely for pure initial-value problems. However, in many laboratory and field situations, the solution is generated by what corresponds to the imposition of boundary conditions rather than initial conditions. Thus, an understanding of BVPs is crucial.
In an exciting sequence of events taking place in the last two decades, new tools have become available to deal with BVPs for integrable PDEs. Although some important issues have already been resolved, several major problems remain open.
The aim of this project is to solve a number of these open problems and to find solutions of BVPs which were heretofore not solvable. More precisely, the proposal has eight objectives:
1. Develop methods for solving problems with time-periodic boundary conditions.
2. Answer some long-standing open questions raised by series of wave-tank experiments 35 years ago.
3. Develop a new approach for the study of space-periodic solutions.
4. Develop new approaches for the analysis of BVPs for equations with 3 x 3-matrix Lax pairs.
5. Derive new asymptotic formulas by using a nonlinear version of the steepest descent method.
6. Construct disk and disk/black-hole solutions of the stationary axisymmetric Einstein equations.
7. Solve a BVP in Einstein's theory of relativity describing two colliding gravitational waves.
8. Extend the above methods to BVPs in higher dimensions.
Max ERC Funding
2 000 000 €
Duration
Start date: 2016-05-01, End date: 2021-04-30
Project acronym DALDECS
Project Development and Application of Laser Diagnostic Techniques for Combustion Studies
Researcher (PI) Lars Eric Marcus Aldén
Host Institution (HI) LUNDS UNIVERSITET
Call Details Advanced Grant (AdG), PE8, ERC-2009-AdG
Summary This project is directed towards development of new laser diagnostic techniques and a deepened physical understanding of more established techniques, aiming at new insights in phenomena related to combustion processes. These non-intrusive techniques with high resolution in space and time, will be used for measurements of key parameters, species concentrations and temperatures. The techniques to be used are; Non-linear optical techniques, mainly Polarization spectroscopy, PS. PS will mainly be developed for sensitive detection with high spatial resolution of "new" species in the IR region, e.g. individual hydrocarbons, toxic species as well as alkali metal compounds. Multiplex measurements of these species and temperature will be developed as well as 2D visualization. Quantitative measurements with high precision and accuracy; Laser induced fluorescence and Rayleigh/Raman scattering will be developed for quantitative measurements of species concentration and 2D temperatures. Also a new technique will be developed for single ended experiments based on picosecond LIDAR. Advanced imaging techniques; New high speed (10-100 kHz) visualization techniques as well as 3D and even 4D visualization will be developed. In order to properly visualize dense sprays we will develop Ballistic Imaging as well as a new technique based on structured illumination of the area of interest for suppression of multiple scattering which normally cause blurring effects. All techniques developed above will be used for key studies of phenomena related to various combustion phenomena; turbulent combustion, multiphase conversion processes, e.g. spray combustion and gasification/pyrolysis of solid bio fuels. The techniques will also be applied for development and physical understanding of how combustion could be influenced by plasma/electrical assistance. Finally, the techniques will be prepared for applications in industrial combustion apparatus, e.g. furnaces, gasturbines and IC engines
Summary
This project is directed towards development of new laser diagnostic techniques and a deepened physical understanding of more established techniques, aiming at new insights in phenomena related to combustion processes. These non-intrusive techniques with high resolution in space and time, will be used for measurements of key parameters, species concentrations and temperatures. The techniques to be used are; Non-linear optical techniques, mainly Polarization spectroscopy, PS. PS will mainly be developed for sensitive detection with high spatial resolution of "new" species in the IR region, e.g. individual hydrocarbons, toxic species as well as alkali metal compounds. Multiplex measurements of these species and temperature will be developed as well as 2D visualization. Quantitative measurements with high precision and accuracy; Laser induced fluorescence and Rayleigh/Raman scattering will be developed for quantitative measurements of species concentration and 2D temperatures. Also a new technique will be developed for single ended experiments based on picosecond LIDAR. Advanced imaging techniques; New high speed (10-100 kHz) visualization techniques as well as 3D and even 4D visualization will be developed. In order to properly visualize dense sprays we will develop Ballistic Imaging as well as a new technique based on structured illumination of the area of interest for suppression of multiple scattering which normally cause blurring effects. All techniques developed above will be used for key studies of phenomena related to various combustion phenomena; turbulent combustion, multiphase conversion processes, e.g. spray combustion and gasification/pyrolysis of solid bio fuels. The techniques will also be applied for development and physical understanding of how combustion could be influenced by plasma/electrical assistance. Finally, the techniques will be prepared for applications in industrial combustion apparatus, e.g. furnaces, gasturbines and IC engines
Max ERC Funding
2 466 000 €
Duration
Start date: 2010-02-01, End date: 2015-01-31
Project acronym DISCONV
Project DISCRETE AND CONVEX GEOMETRY: CHALLENGES, METHODS, APPLICATIONS
Researcher (PI) Imre Barany
Host Institution (HI) MAGYAR TUDOMANYOS AKADEMIA RENYI ALFRED MATEMATIKAI KUTATOINTEZET
Call Details Advanced Grant (AdG), PE1, ERC-2010-AdG_20100224
Summary Title: Discrete and convex geometry: challenges, methods, applications
Abstract: Research in discrete and convex geometry, using tools from combinatorics, algebraic
topology, probability theory, number theory, and algebra, with applications in theoretical
computer science, integer programming, and operations research. Algorithmic aspects are
emphasized and often serve as motivation or simply dictate the questions. The proposed
problems can be grouped into three main areas: (1) Geometric transversal, selection, and
incidence problems, including algorithmic complexity of Tverberg's theorem, weak
epsilon-nets, the k-set problem, and algebraic approaches to the Erdos unit distance problem.
(2) Topological methods and questions, in particular topological Tverberg-type theorems,
algorithmic complexity of the existence of equivariant maps, mass partition problems, and the
generalized HeX lemma for the k-coloured d-dimensional grid. (3) Lattice polytopes and random
polytopes, including Arnold's question on the number of convex lattice polytopes, limit
shapes of lattice polytopes in dimension 3 and higher, comparison of random polytopes and
lattice polytopes, the integer convex hull and its randomized version.
Summary
Title: Discrete and convex geometry: challenges, methods, applications
Abstract: Research in discrete and convex geometry, using tools from combinatorics, algebraic
topology, probability theory, number theory, and algebra, with applications in theoretical
computer science, integer programming, and operations research. Algorithmic aspects are
emphasized and often serve as motivation or simply dictate the questions. The proposed
problems can be grouped into three main areas: (1) Geometric transversal, selection, and
incidence problems, including algorithmic complexity of Tverberg's theorem, weak
epsilon-nets, the k-set problem, and algebraic approaches to the Erdos unit distance problem.
(2) Topological methods and questions, in particular topological Tverberg-type theorems,
algorithmic complexity of the existence of equivariant maps, mass partition problems, and the
generalized HeX lemma for the k-coloured d-dimensional grid. (3) Lattice polytopes and random
polytopes, including Arnold's question on the number of convex lattice polytopes, limit
shapes of lattice polytopes in dimension 3 and higher, comparison of random polytopes and
lattice polytopes, the integer convex hull and its randomized version.
Max ERC Funding
1 298 012 €
Duration
Start date: 2011-04-01, End date: 2017-03-31
Project acronym DISCRETECONT
Project From discrete to contimuous: understanding discrete structures through continuous approximation
Researcher (PI) László Lovász
Host Institution (HI) EOTVOS LORAND TUDOMANYEGYETEM
Call Details Advanced Grant (AdG), PE1, ERC-2008-AdG
Summary Important methods and results in discrete mathematics arise from the interaction between discrete mathematics and ``continuous'' areas like analysis or geometry. Classical examples of this include topological methods, linear and semidefinite optimization generating functions and more. More recent areas stressing this connection are the theory of limit objects of growing sequences of finite structures (graphs, hypergraphs, sequences), differential equations on networks, geometric representations of graphs. Perhaps most promising is the study of limits of growing graph and hypergraph sequences. In resent work by the Proposer and his collaborators, this area has found highly nontrivial connections with extremal graph theory, the theory of property testing in computer science, to additive number theory, the theory of random graphs, and measure theory as well as geometric representations of graphs. This proposal's goal is to explore these interactions, with the participation of a number of researchers from different areas of mathematics.
Summary
Important methods and results in discrete mathematics arise from the interaction between discrete mathematics and ``continuous'' areas like analysis or geometry. Classical examples of this include topological methods, linear and semidefinite optimization generating functions and more. More recent areas stressing this connection are the theory of limit objects of growing sequences of finite structures (graphs, hypergraphs, sequences), differential equations on networks, geometric representations of graphs. Perhaps most promising is the study of limits of growing graph and hypergraph sequences. In resent work by the Proposer and his collaborators, this area has found highly nontrivial connections with extremal graph theory, the theory of property testing in computer science, to additive number theory, the theory of random graphs, and measure theory as well as geometric representations of graphs. This proposal's goal is to explore these interactions, with the participation of a number of researchers from different areas of mathematics.
Max ERC Funding
739 671 €
Duration
Start date: 2009-01-01, End date: 2014-06-30
Project acronym ELSI
Project Emotional Learning in Social Interaction
Researcher (PI) Andreas Olsson
Host Institution (HI) KAROLINSKA INSTITUTET
Call Details Starting Grant (StG), SH4, ERC-2011-StG_20101124
Summary This project will open up new horizons in the study of emotional learning by describing and modeling its role in social interaction. It brings together a novel set of experimental manipulations with two hitherto unconnected lines of research; biology of aversive learning and social cognition, with the aim to answer four specific objectives, namely to identify the mechanisms of aversive learning (1) about others and its dependence on stimulus bound (e.g. ethnic group belonging) and conceptual (e.g. moral and social status) features; (2) from others through observation, and its dependence on processing of stimulus bound (e.g. emotional expressiveness) and conceptual (e.g. empathy and mental state attributions) features; (3) during interaction and its dependence social characteristics as described in 1 and 2; and (4) build and test a neural model of social-emotional learning. To achieve these objectives, this project proposes a multi-method research program using novel behavioral experimental paradigms and manipulated virtual environments, drawing on cognitive neuroscience, psychophysiology, and behavioral genetics. It is predicted that social emotional learning will be accomplished through the interaction of four, partially overlapping, neural networks coding for affective, associative, social cognitive and instrumental/goal directed aspects, respectively. Whereas it is expected that the two first networks will be common to classical conditioning and social learning, the latter is hypothesized to be distinguished by its reliance on the social-cognitive network. The fourth network is predicted to be integral to the social learning through interactions and the shaping of behavioral norms. The proposed research will enhance our understanding of important social phenomena, such as the emergence and maintanance of group conflicts and norm compliance. It will also shed light on common psychological disorders, such as social anxiety, autism and psychopathy that are characterized by dysfunctions of the social emotional learning system.
Summary
This project will open up new horizons in the study of emotional learning by describing and modeling its role in social interaction. It brings together a novel set of experimental manipulations with two hitherto unconnected lines of research; biology of aversive learning and social cognition, with the aim to answer four specific objectives, namely to identify the mechanisms of aversive learning (1) about others and its dependence on stimulus bound (e.g. ethnic group belonging) and conceptual (e.g. moral and social status) features; (2) from others through observation, and its dependence on processing of stimulus bound (e.g. emotional expressiveness) and conceptual (e.g. empathy and mental state attributions) features; (3) during interaction and its dependence social characteristics as described in 1 and 2; and (4) build and test a neural model of social-emotional learning. To achieve these objectives, this project proposes a multi-method research program using novel behavioral experimental paradigms and manipulated virtual environments, drawing on cognitive neuroscience, psychophysiology, and behavioral genetics. It is predicted that social emotional learning will be accomplished through the interaction of four, partially overlapping, neural networks coding for affective, associative, social cognitive and instrumental/goal directed aspects, respectively. Whereas it is expected that the two first networks will be common to classical conditioning and social learning, the latter is hypothesized to be distinguished by its reliance on the social-cognitive network. The fourth network is predicted to be integral to the social learning through interactions and the shaping of behavioral norms. The proposed research will enhance our understanding of important social phenomena, such as the emergence and maintanance of group conflicts and norm compliance. It will also shed light on common psychological disorders, such as social anxiety, autism and psychopathy that are characterized by dysfunctions of the social emotional learning system.
Max ERC Funding
1 498 244 €
Duration
Start date: 2012-12-01, End date: 2018-11-30
Project acronym EPIDELAY
Project Delay differential models and transmission dynamics of infectious diseases
Researcher (PI) Gergely Röst
Host Institution (HI) SZEGEDI TUDOMANYEGYETEM
Call Details Starting Grant (StG), PE1, ERC-2010-StG_20091028
Summary The aim of this project is to develop and analyse infinite dimensional dynamical models for the transmission dynamics and propagation of infectious diseases. We use an integrated approach which spans from the abstract theory of functional differential equations to the practical problems of epidemiology, with serious implications to public health policy, prevention, control and mitigation strategies in cases such as the ongoing battle against the nascent H1N1 pandemic.
Delay differential equations are one of the most powerful mathematical modeling tools and they arise naturally in various applications from life sciences to engineering and physics, whenever temporal delays are important. In abstract terms, functional differential equations describe dynamical systems, when their evolution depends on the solution at prior times.
The central theme of this project is to forge strong links between the abstract theory of delay differential equations and practical aspects of epidemiology. Our research will combine competencies in different fields of mathematics and embrace theoretical issues as well as real life applications.
In particular, the theory of equations with state dependent delays is extremely challenging, and this field is at present on the verge of a breakthrough. Developing new theories in this area and connecting them to relevant applications would go far beyond the current research frontier of mathematical epidemiology and could open a new chapter in disease modeling.
Summary
The aim of this project is to develop and analyse infinite dimensional dynamical models for the transmission dynamics and propagation of infectious diseases. We use an integrated approach which spans from the abstract theory of functional differential equations to the practical problems of epidemiology, with serious implications to public health policy, prevention, control and mitigation strategies in cases such as the ongoing battle against the nascent H1N1 pandemic.
Delay differential equations are one of the most powerful mathematical modeling tools and they arise naturally in various applications from life sciences to engineering and physics, whenever temporal delays are important. In abstract terms, functional differential equations describe dynamical systems, when their evolution depends on the solution at prior times.
The central theme of this project is to forge strong links between the abstract theory of delay differential equations and practical aspects of epidemiology. Our research will combine competencies in different fields of mathematics and embrace theoretical issues as well as real life applications.
In particular, the theory of equations with state dependent delays is extremely challenging, and this field is at present on the verge of a breakthrough. Developing new theories in this area and connecting them to relevant applications would go far beyond the current research frontier of mathematical epidemiology and could open a new chapter in disease modeling.
Max ERC Funding
796 800 €
Duration
Start date: 2011-05-01, End date: 2016-12-31
Project acronym INSYSBIO
Project Industrial Systems Biology of Yeast and A. oryzae
Researcher (PI) Jens Nielsen
Host Institution (HI) CHALMERS TEKNISKA HOEGSKOLA AB
Call Details Advanced Grant (AdG), PE8, ERC-2009-AdG
Summary Metabolic engineering is the development of new cell factories or improving existing ones, and it is the enabling science that allows for sustainable production of fuels and chemicals through biotechnology. With the development in genomics and functional genomics, it has become interesting to evaluate how advanced high-throughput experimental techniques (transcriptome, proteome, metabolome and fluxome) can be applied for improving the process of metabolic engineering. These techniques have mainly found applications in life sciences and studies of human health, and it is necessary to develop novel bioinformatics techniques and modelling concepts before they can provide physiological information that can be used to guide metabolic engineering strategies. In particular it is challenging how these techniques can be used to advance the use of mathematical modelling for description of the operation of complex metabolic networks. The availability of robust mathematical models will allow a wider use of mathematical models to drive metabolic engineering, in analogy with other fields of engineering where mathematical modelling is central in the design phase. In this project the advancement of novel concepts, models and technologies for enhancing metabolic engineering will be done in connection with the development of novel cell factories for high-level production of different classes of products. The chemicals considered will involve both commodity type chemicals like 3-hydroxypropionic acid and malic acid, that can be used for sustainable production of polymers, an industrial enzyme and pharmaceutical proteins like human insulin.
Summary
Metabolic engineering is the development of new cell factories or improving existing ones, and it is the enabling science that allows for sustainable production of fuels and chemicals through biotechnology. With the development in genomics and functional genomics, it has become interesting to evaluate how advanced high-throughput experimental techniques (transcriptome, proteome, metabolome and fluxome) can be applied for improving the process of metabolic engineering. These techniques have mainly found applications in life sciences and studies of human health, and it is necessary to develop novel bioinformatics techniques and modelling concepts before they can provide physiological information that can be used to guide metabolic engineering strategies. In particular it is challenging how these techniques can be used to advance the use of mathematical modelling for description of the operation of complex metabolic networks. The availability of robust mathematical models will allow a wider use of mathematical models to drive metabolic engineering, in analogy with other fields of engineering where mathematical modelling is central in the design phase. In this project the advancement of novel concepts, models and technologies for enhancing metabolic engineering will be done in connection with the development of novel cell factories for high-level production of different classes of products. The chemicals considered will involve both commodity type chemicals like 3-hydroxypropionic acid and malic acid, that can be used for sustainable production of polymers, an industrial enzyme and pharmaceutical proteins like human insulin.
Max ERC Funding
2 499 590 €
Duration
Start date: 2010-01-01, End date: 2014-12-31
Project acronym InvGroGra
Project Asymptotic invariants of discrete groups, sparse graphs and locally symmetric spaces
Researcher (PI) Miklos Abert
Host Institution (HI) MAGYAR TUDOMANYOS AKADEMIA RENYI ALFRED MATEMATIKAI KUTATOINTEZET
Call Details Consolidator Grant (CoG), PE1, ERC-2014-CoG
Summary The PI proposes to study the asymptotic behavior of various invariants of discrete groups and their actions, of sparse graphs and of locally symmetric spaces. The game is to connect the asymptotic behavior of an invariant on a sequence of finite models to an analytic invariant on a suitable limit object of the sequence and then use the connection to get new results in both the finite and infinite worlds. The recently emerging notion of invariant random subgroups, initiated by the PI, serves as a unifying language for convergence.
These invariants include the minimal number of generators, deficiency, Betti numbers over arbitrary fields, various spectral and representation theoretic invariants, graph polynomials and entropy. The limit objects arising are invariant processes on groups, profinite actions, graphings, invariant random subgroups and measured complexes. The analytic invariants include L2 Betti numbers, spectral and Plancherel measures, cost and its higher order versions, matching and chromatic measures and entropy per site.
Energy typically flows both ways between the finite and infinite world and also between the different invariants. We list five recent applications from the PI that emerged from such connections. 1) Any large volume locally symmetric semisimple space has large injectivity radius at most of its points; 2) The rank gradient of a chain equals the cost-1 of the profinite action of the chain; 3) Countable-to-one cellular automata over a sofic group preserve the Lebesque measure; 4) Ramanujan graphs have essentially large girth; 5) The matching measure is continuous for graph convergence, giving new estimates on monomer-dimer free energies.
Besides asymptotic group theory and graph theory, the tools of the proposed research come from probability theory, ergodic theory and statistical mechanics. The proposed research will lead to further applications in 3-manifold theory, geometry and ergodic theory.
Summary
The PI proposes to study the asymptotic behavior of various invariants of discrete groups and their actions, of sparse graphs and of locally symmetric spaces. The game is to connect the asymptotic behavior of an invariant on a sequence of finite models to an analytic invariant on a suitable limit object of the sequence and then use the connection to get new results in both the finite and infinite worlds. The recently emerging notion of invariant random subgroups, initiated by the PI, serves as a unifying language for convergence.
These invariants include the minimal number of generators, deficiency, Betti numbers over arbitrary fields, various spectral and representation theoretic invariants, graph polynomials and entropy. The limit objects arising are invariant processes on groups, profinite actions, graphings, invariant random subgroups and measured complexes. The analytic invariants include L2 Betti numbers, spectral and Plancherel measures, cost and its higher order versions, matching and chromatic measures and entropy per site.
Energy typically flows both ways between the finite and infinite world and also between the different invariants. We list five recent applications from the PI that emerged from such connections. 1) Any large volume locally symmetric semisimple space has large injectivity radius at most of its points; 2) The rank gradient of a chain equals the cost-1 of the profinite action of the chain; 3) Countable-to-one cellular automata over a sofic group preserve the Lebesque measure; 4) Ramanujan graphs have essentially large girth; 5) The matching measure is continuous for graph convergence, giving new estimates on monomer-dimer free energies.
Besides asymptotic group theory and graph theory, the tools of the proposed research come from probability theory, ergodic theory and statistical mechanics. The proposed research will lead to further applications in 3-manifold theory, geometry and ergodic theory.
Max ERC Funding
1 386 250 €
Duration
Start date: 2015-07-01, End date: 2020-06-30