Prof Dr George Lake
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Institute for Theoretical Physics University of Zürich Winterthurerstr. 190 8057 Zürich Switzerland +41 44 635 6198, Office: 36 L 08 |
Research
Primary research interests:
Formation and Evolution of Large Scale Structure: Our simulations are designed to use every probe of Large Scale Structure including: properties of clusters of galaxies, the structure of the local group, statistics of QSO absorbers and surveys like the Sloan Digital Sky Survey. Both the Sloan Survey and the Netherlands Foundation for Radio Astronomy are using our simulations to construct their long term plans.
Formation and Early Evolution of Galaxies: The appearance of galaxies at redshifts of up to 2 will become even more interesting with the advent of 8-meter ground based telescopes and a properly working HST. The UW HPCC group works on providing accurate models of the evolution of the Universe at moderate redshifts.
Evolution of Our Solar System, Implications for the Search for Other Planetary Systems: We are integrating the solar system for its lifetime; the longest previous integration is 6 Myr. The Lyapanov exponent of the inner planetary system is just 5 Myr. Our integration will address problems concerning weak chaos, the astrophysical impact on climate and the stability of the solar system.
The Formation of Globular Clusters: I have a new explanation for the mass function of clusters that relies only on atomic physics and new calculations that show that the shape of the velocity ellipsoid constrains mass loss.
Spatially and Temporally Adaptive Parallel Algorithms for gravity and hydro. Current work includes: methods of potential calculation; algorithmic and domain decomposition; time adaptive symplectic integration; smoothed particle hydro. Our codes are efficient and portable despite solving tightly coupled problems with adaptive methods.
Building Community Frameworks for Simulation and Analysis: Architectures have changed rapidly making it necessary to build good abstractions and modules to rapidly port to new systems. MPPs are a memory resource with barely enough computer power to drive that memory, so our simulations have typically filled the memory of the system and our codes have been designed to use little memory beyond that needed to characterize the state of the system. As a result, data set sizes challenge our analysis paradigm. I formed the Whole N -Chilada Project to bring together the community that does particle simulation to build a parallel simulation and analysis framework. As NASA Project Scientist for High Performance Computing and Communication for Earth and Space Science (NASA HPCC/ESS), I was the key advocate of the Earth System Modeling Framework and the architect of the solicitation to build it. I was also lead author on the white paper that started the Digital Sky (National Virtual Observatory) project.
Commodity and High End Supercomputing: Beowulf was launched from HPCC/ESS and my UW group was the first to build a commodity cluster from alpha nodes. This has been extremely important for demonstrating the ability of parallel supercomputing to scale down as well as up. I have also been instrumental in demonstrating that some problems that can only be solved on tightly coupled, large shared memory machines.
Precision and Supercomputing: I very interested in the problem of the precision needed to solve scientific problems and how this will likely impact future machines.
Million-way Parallelism and Fault Tolerant Algorithms: like the previous item, thinking ahead to things that will be essential in a decade or two.
Whole Genome Evolution and the Role of Retroviruses: I’ve been examining the role of retroviruses in speciation and “explosive” events like the mammalian radiation and the Cambrian explosion.
My specific research accomplishments to date include:
Galaxy harassment and its consequences including the rapid evolution of galaxies in clusters. This result came from calculating the expected physical heating of galaxies within clusters and insuring that the numerical heating was at least an order of magnitude less. As a result, a new physical effect was discovered and numerical artifacts were debunked. Understanding galaxy harassment led to the resolution of problems in galaxy morphology and activity within clusters that had existed for over 25 years. Verification of the numerous detailed predictions occupied a large fraction of time on the world’s largest telescopes for a few years.
Development of “volume renormalization” as a technique to simulate objects of cosmological importance (galaxies, clusters of galaxies, early QSO hosts) in proper cosmological context.
Development of a time adaptive symplectic integrator.
Building the first disk galaxies in renormalized cosmological simulations. The inability to make disks in cosmological simulations had been touted for years as the “bayron catastrophe”, but was merely a numerical artifact of extreme viscosity in numerical simulations.
Performing the first simulations of clusters of galaxies where the galaxies did not spontaneously detonate, but remained intact with a mass function that matched observed clusters of galaxies. For decades, the dissolution of galaxies during the formation of clusters was thought to be physical and was lamented as the “overmerging problem”. Spontaneous detonation of galaxies was as overrated as spontaneous detonation of people.
New techniques for building self-consistent models of galaxies.
Demonstration of the existence of tilted disks in some triaxial potentials.
A dynamical test for the intrinsic shape of galaxies.
A stability criteria for galaxies that is applicable rather than universal.
Analysis of binary pairs of dwarf galaxies finding large masses.
New techniques for analyzing rotation curves that yield rigorous limits on halo properties.
Prediction of a greater degree of rotational support in low luminosity ellipticals.
Prediction and observational confirmation of a greater frequency of HI in low luminosity ellipticals.
Large numerical simulations lead to the discovery of a control parameter for the Hubble sequence. Support for the scenario has been found in observed properties of dark halos.
The proposal that QSO absorption line systems are the products of thermally unstable protogalaxies. Construction of a test using He+ l304 and HeI l584 lines to distinguish among all current models of such systems.
Observations of the luminosity-velocity relation in merger remnants—the first use of the Ca triplet to observe the dynamics of the old stellar populations in star-forming galaxies.
The discovery of dark galaxies—dwarf galaxies with the masses of bright galaxies.
Demonstrating that dark matter cannot be replaced with changes in the law of gravity.