Abstracts of talks and biographical information

You will find on this page abstracts of talks that I am currently giving, as well as biographical information. This information is provided for the convenience of institutions where I am giving seminars or colloquia.  Talks marked as COLLOQUIUM are suitable for a general audience including graduate students and advanced undergraduates, although I have given them as seminars too.  Talks marked as SEMINAR are intended for a more specialised audience.

COLLOQUIUM

My Manhattan Project: A Physicist's Adventures on Wall St

Why is Wall St. one of the biggest employers of physicists? What is the quickest way to lose a billion dollars? How might academic physicists gain experience of real world applications? And why bother? I discuss these and other questions in light of my own experience, starting a software company to market ultra-fast tools for risk management of derivative securities.

COLLOQUIUM

Biocomplexity in Action: Pattern Formation and Microbial Ecology at Yellowstone's Hot Springs

Abstract

Biocomplexity is the term that is becoming used to describe efforts to understand strongly-interacting dynamical systems with a biological, ecological or even social component.  I provide a brief overview of why this field is not only interesting for physicists, but can benefit substantially from their participation.  In particular, microbes represent a fascinating opportunity for physicists to contribute to biology, because their strong interactions, via both signalling and exchange of genes, means that the techniques of statistical mechanics are ideally suited to exploring the ecology of microbial communities and the evolutionary dynamics of microbial genomes.

As a case study of biocomplexity, I present my own work on geobiological pattern formation at Yellowstone's Mammoth Hot Springs, where heat-loving microbes may play a role in the dynamics of landscape evolution. I'll describe my group's recent field, experimental and theoretical work on the possible role of microbes in creating scale-invariant travertine terraces at geothermal hot springs. The ability to distinguish both ancient and modern geological features that are biologically influenced from those that are purely abiotic in origin can potentially advance our understanding of the timing and pattern of evolution, and may even provide a tool with which to identify evidence for life on other planets.

Work performed in collaboration with: G. Bonheyo, J. Frias-Lopez, H. Garcia Martin, J. Veysey, B. Fouke.
Work supported by the US National Science Foundation.

COLLOQUIUM

Patterns, universality and computational algorithms

Can we use computational algorithms to make accurate predictions of physical phenomena?  In this talk, intended for non-experts, I will give examples where complicated space-time phenomena can be exquisitely captured with simple computational algorithms, that not only produce patterns resembling those seen in experiment, but also make accurate predictions about probes of dynamics and spatial organisation, such as correlation functions.  I use examples from condensed matter physics, as well as from geophysics.

Because many patterns involve structure on multiple length and time scales, I also discuss how one can develop multiscale methods for real materials processing from the nanoscale on up.  I show that a computationally-efficient multiscale approach can be developed systematically by using renormalization group or equivalent techniques to derive appropriate coupled phase and amplitude equations, which can then be solved by adaptive mesh refinement algorithms.

Work supported by National Science Foundation and NASA.

COLLOQUIUM

What does the genetic code tell us about early life?

OR

Statistical mechanics of the genetic code: a glimpse of early life?

Relics of early life, preceding even the last universal common ancestor of all life on Earth, are present in the structure of the modern day canonical genetic code. In this talk, I will draw attention to these relics, and discuss their interpretation from the perspective of the dynamical system that is evolution. I will argue that this viewpoint, and the quantitative, statistical dynamical calculations that it entails, suggest a natural scenario in which evolution exhibits three distinct dynamical regimes, differentiated respectively by the way in which information flow, genetic novelty and complexity emerge. Possible observational signatures of these predictions are discussed.

Reference: K. Vetsigian, C.R. Woese and Nigel Goldenfeld. Communal evolution of the genetic code. Proc. Natl. Acad. Sci. 103 , 10696-10701 (2006) .

SEMINAR

Statistical mechanics of genes: an emergent mechanism for speciation in microbes

I show that strongly-interacting communities of microbes exhibit a non-trivial phase diagram that depends upon the details of homologous recombination and the competition with point mutation.  Possible phases include one that is genetically uniform, and another that is biodiverse.  A comparative genomic study of sequenced, closely-related microbial genomes finds evidence for the predicted signature of this phase transition in Bacillus.  This work highlights the important role that emergent, collective effects can play in determining microbial community structure and speciation.

SEMINAR

Pairing and critical phenomena in the cuprate superconductors

I describe how measurements of the electromagnetic penetration depth in cuprate superconductors have not only provided the first evidence for d-wave pairing, but have also provided the strongest example of three dimensional critical phenomena of the superconducting transition, beyond Gaussian fluctuations.  This talk will cover work performed in collaboration with D. Bonn and W. Hardy on statics, and very recent observations of critical dynamics performed with D. Van Harlingen and J. Eckstein.  I will also explain the paradoxical results of Monte Carlo simulations that seemed to suggest that the dynamic critical exponent was less than 2, i.e. contradicting the notion that the time-dependent Ginzburg-Landau equations were the appropriate starting point for the dynamics.

SEMINAR

Beyond phase field models: renormalization group approach to multiscale modeling in materials science

Dendritic growth, and the formation of material microstructure in general, necessarily involves a wide range of length scales from the atomic up to sample dimensions.  Phase field models, enhanced by optimal asymptotic methods and adaptive mesh refinement, cope with this range of scales, and provide a very efficient way to move phase boundaries.  However, they fail to preserve memory of the underlying crystallographic anisotropy.  Elder and Grant have convincingly shown how one can use the phase field crystal (PFC) equation -- a conserving analogue of the Swift-Hohenberg equation -- to create field equations with periodic solutions that model elasticity, the formation of solid phases, and accurately reproduce the nonequilibrium dynamics of phase transitions in real materials.  In this talk, I show that a computationally-efficient multiscale approach to the PFC can be developed systematically by using the renormalization group or equivalent techniques to derive the appropriate coupled phase and amplitude equations, which can then be solved by adaptive mesh refinement algorithms.

SEMINAR

Renormalization Group Approach to Global Asymptotic Analysis

Renormalization and the renormalization group (RG) were originally developed by physicists attempting to understand the divergent terms in perturbation theory and the short distance behaviour of quantum electrodynamics. During the last few years, these methods have been used to study the divergent terms in perturbation theory and the long time behaviour of a variety of nonlinear partial differential equations. Problems studied include similarity solutions, especially intermediate asymptotics of the second kind (Barenblatt classification), and travelling waves. Examples include: porous medium equation, propagation of turbulence and the Fisher-Kolmogorov-Petrovsky-Piskunov equation.

Most recently, singular perturbation problems for nonlinear differential equations have been treated, with particular attention paid to multiple-scale analysis, boundary layers and WKB, and matched asymptotics.

The RG method starts from a regular perturbation expansion in the small parameter, and automatically generates an asymptotic sequence without requiring the user to make insightful guesses as to the presence of "unexpected" powers, logarithms, etc. The RG-generated uniform approximation is practically more useful than that generated by matched asymptotics, even when extended to values of the small parameter of order unity.

Reference:

Work performed in collaboration with Yoshitsugu Oono, L.-Y. Chen, O. Martin, F. Liu.

Please note: A longer and more detailed version of the material in this talk and that in my talk on Under-resolved Computation has also been given as a mini-course of 3 lectures, including topics such as similarity solutions and anomalous dimensions, front propagation and RG.

SEMINAR

Turbulence!

Turbulence is usually characterized by scaling, energy cascade and intermittency, concepts which are presented in the concepts of complex systems not usually thought of as being related to fluid dynamics.  This talk discusses whether or not turbulence is ever fully-developed at a finite Reynolds number, by analogy with recent work on anomalous scaling in the (mean velocity)-(distance from wall) relationship found in pipe flow.  I discuss recent experimental observations that the probability distribution of power fluctuations has a universal form, apparently indistinguishable from that seen in the 2D XY model well below the Kosterlitz-Thouless transition. Lastly, I present evidence from a reanalysis of turbulent pipe flow in smooth and rough pipes for a complete analogy between turbulence and critical phenomena, going beyond power-law scaling in spectral structure.

References:

Biographical information

Nigel Goldenfeld is a Professor of Physics at the University of Illinois at Urbana-Champaign and leads the Biocomplexity group at the University's Institute for Genomic Biology. He received his Ph.D. from the University of Cambridge (U.K.) in 1982, and for the years 1982-1985 was a postdoctoral fellow at the Institute for Theoretical Physics, University of California at Santa Barbara. Nigel has been an Alfred P. Sloan Foundation Fellow, a University Scholar of the University of Illinois, a recipient of the Xerox Award for research, and a recipient of the A. Nordsieck award for excellence in graduate teaching. In 1996, Nigel co-founded NumeriX, a company that specializes in high-performance software for the derivatives marketplace.   He is a member of the Editorial Board of the International Journal of Theoretical and Applied Finance and is a Fellow of the American Physical Society.

Updated Jan 2007
Nigel Goldenfeld