Computations in Science Seminars
Oct
22
Wed 12:15
Andy Ruina, Cornell
e-mail:
Host: Leo Kadanoff ()
Non-holonomic stability and rotation with zero angular momentum: Demonstrations of stability and of the falling cat phenomenon go sour.

This talk is about two classes of (interesting, at least to me) physical behavior that follow from them impossibility of integrating some formulas that involve derivatives. First, systems with wheels or ice skates can be conservative yet have asymptotic stability. This is relevant to braking cars, flying arrows and the balance of skateboards and bicycles. Second, is the well known possibility that a system with zero angular momentum can, by appropriate deformations, rotate without any external torque. This effect explains how a cat that is dropped while upside down can turn over and of how various gymnastic maneuvers are performed. Both rolling contact and constancy of angular momentum are examples of the "non-integrability" of a "non-holonomic" equation. There are various simple demonstrations of these phenomena that can go bad. Cars can crash, bikes fall over and, in terrestrial experiments, various effects can swamp that which one wants to demonstrate. The talk describes the basic theory and then a collection of simple experiments that fail various ways for various reasons.

Oct
23
Thu 5:30 PM
Francesca Casadio, Art Institute of Chicago
e-mail:
Apolinère Enameled: Enamel Paints and the Making of Avant-Garde Art
Special seminar at the Department of Art History, Cochrane Woods Art Center, Room 157 (5540 S. Greenwood Avenue)

Oil-based enamel paints, manufactured for household and other uses in the beginning of the twentieth century became popular among avant-garde European painters because of their surface qualities and handling properties: Pablo Picasso, Wassily Kandinsky, Francis Picabia, René Magritte and others are reported to have used Ripolin house paints in their works. These paints were so renowned that the term ‘ripolin’ was often used to refer to a broader class of enamel paints in general and soon became synonymous with modernity, sophisticated technology, excellent quality and high performance. Surprisingly, little attention has been given to the study of industrial paint chemistry and technology including house, architectural, car and boat paints produced in the beginning of the twentieth century. For the past several years a research project has been carried out at the Art Institute of Chicago to fill this gap, approaching the study through sophisticated scientific analysis, in-depth study of the industrial technical literature of the time, and analysis of paintings by Pablo Picasso and his contemporaries.

The analysis of artists’ paints, hierarchically complex materials typically composed of binder, pigments, fillers, and other additives is a challenging, multiscale problem. Techniques as simple as visual observation under a visible light stereomicroscope and as complex as high resolution nanoprobe Synchrotron Radiation-X-ray fluorescence (SR-XRF) mapping are deployed by museum scientists to answer questions about composition, stability, manufacturing technology, and even the artist’s intention.

For the past eleven years a state of the art scientific laboratory has been developed at the Art Institute of Chicago to enhance our understanding and long-term preservation of the works in the collection. In this talk Dr. Casadio will present a behind the scenes look at the research taking place in preparation for exhibitions and scholarly catalogues. Part forensic science, part detective work, this lecture will unravel the creative and technical feats of art giants such as Pablo Picasso. It will illuminate how the tools of science and archival research into technical and industrial sources can shed new light on the work of conservators and art historians and potentially alter the way in which the public looks at each work of art.

Oct
27
Mon 12:15
Dmitry Green, Saba Capital
e-mail:
Host: Leo Kadanoff ()
Employment Paths for Physicists - a UofC Grad's experience

This will be one person's take on the spectrum of career paths outside of physics. I will discuss my own experience,and where the next opportunities seem to be headed. Much of my experience has been in the financial sector so I will focus on it. Finance happens to be in the midst of massive changes and the opportunities of the past are not likely to be the opportunities of the future. I've also had the opportunity to see various transitions from academia to business and will offer examples of what has worked and not worked (including my mistakes!).

Oct
28
Tue 3:00 PM
Srikanth Sastry, Jawaharlal Nehru Centre
e-mail:
Host: Sidney Nagel ()
Yielding, jamming and memory in sheared amorphous solids and fluids

A microscopic understanding of their mechanical response, and flow under applied stress, of amorphous solids is of considerable current interest. Computational investigations of the response of model amorphous solids reveals rich phenomenology and provide insights into the nature of the yielding of such solids. A dynamical transition, related to yielding, is observed when the amplitude of oscillatory shear deformation is varied: For large values of the amplitude the system exhibits diffusive behavior and loss of memory of the initial conditions, whereas localization -- but with interesting periodic orbits -- is observed for small amplitudes. In the localization regime, interesting memory effects are observed, involving the possibility of storing persistent multiple memories. In hard and soft sphere packings modeling granular matter, instead, shear deformation leads to structures with interesting geometric signatures that are revealed by the analysis of the void space in such structures, and are argued to underlie shear jamming under suitable conditions.

Oct
29
Wed 12:15
Kerry Emanuel, MIT
e-mail:
Host: Leo Kadanoff ()
Radiative-Convective Instability: Implications for Tropical Weather and Climate

The concept of radiative-convective equilibrium (RCE) is the simplest and arguably the most elegant model of a climate system, regarding it as a statistically one-dimensional balance between radiative and convective heat transfer. In spite of this, RCE is seldom studied and poorly understood today. Recent advances in cloud-system-resolving numerical models have made it possible to explicitly simulate such states, simulating the convective plumes themselves rather than representing them parametrically. The simulations reveal a startling phenomenon: Above a critical surface temperature, moist convection spontaneously aggregates into a single cluster, in a non-rotating system, or into multiple tropical cyclones on a rotating planet. I will show that this results from a linear instability of the RCE state, and this this instability migrates the RCE state toward one of the two stable equilibria. This instability represents a subcritical bifurcation of the ordinary RCE state, leading to either a dry state with large-scale descent, or to a moist state with mean ascent; these states may be accessed by finite amplitude perturbations to ordinary RCE in the subcritical state, or spontaneously in the supercritical state.

Nov
5
Wed 12:15
Guenter Ahlers, UC Santa Barbara
e-mail:
Host: Leo Kadanoff ()
Pattern Formation and Turbulence in Convection, the Legacy of Henri Bénard

Over a century ago a 26-year young physicist by the name of Henri Bénard handed in his Ph.D. thesis, entitled Les tourbillons cellulaires dans une nappe liquide, at the Ecole Normale Supérieure in Paris. In a fluid layer with a free upper surface and heated from below he observed and studied remarkably regular hexagonal patterns. I shall attempt to trace the developments in nonlinear physics, and especially in fluid mechanics, that have evolved from Bénard's seminal experiments.

As a result of the work of many, including Lord Rayleigh, Harold Je ries (Sir Harold), W.V.R. Malkus, G. Veronis, and Fritz Busse (2000 Fluid-Dynamics- Prize recipient) a remarkably detailed understanding of the nature of convection in a shallow fluid layer between two solid horizontal confining surfaces and heated from below had been gained by the early 1970's. The bifurcation to convection is stationary and occurs at a temperature difference (in dimensionless form represented by the Rayleigh number Ra) and a wave number k that are non-zero (Rayleigh, Jeffries). The bifurcation is supercritical to a pattern of rolls (Malkus and Veronis; Schlüter, Lortz, and Busse). Above onset there is a finite range in the Ra - k plane, delimited by several interesting instabilities, over which the rolls are stable (Clever and Busse). This region, known now affectionately as the "Busse Balloon", has been used during the last three decades to study both theoretically and experimentally numerous non-linear phenomena, including the role of thermal fluctuations near the bifurcation, the dynamics of pattern coarsening, various wave-number selection processes, spatio-temporal chaos, and spatially localized structures or "pulses".

In somewhat more recent times the range of Ra has been extended up to 10¹⁴ times the critical value Ra_c = O(10³) at onset and a richness of phenomena involving turbulent flows has been revealed and studied quantitatively. One of the particularly interesting issues amenable to study in this system has been the interaction between large-scale flow structures and the small-scale turbulent fluctuations; but there are many other aspects that have provided seemingly endless fascination for the researchers.

Nov
12
Wed 12:15
Mogens Hogh Jensen, University of Copenhagen
e-mail:
Host: Leo Kadanoff ()
Life in Turbulence

Satellite pictures indicate that plankton-life in the oceans exhibit 'foliated' structures on many length scales clearly influenced by the turbulent flows in the water. We formulate a particle model where plankton are advected in a model field of strong turbulence. The model indicates a huge drop in the carrying capacity due high concentrations in the stagnation points of the flow. For two neutral alleles, we find that the presence of turbulence diminishes the fixation time significantly. We further study the fixation time as a function of various flow parameters and obtain analytical expressions for the fixation probability without flows. Simulations of the model in zero and one dimensions give good agreement with theoretical predictions both when species experience competitive exclusions and when they co-exist under mutualistic behavior. We also briefly discuss some general properties of turbulence and shell models.

Nov
19
Wed 12:15
Emil Martinec, University of Chicago
e-mail:
Black Holes and Phases of Matter and Geometry

Black holes are an exquisite testing ground for our understanding of quantum gravity. Particularly vexing puzzles have arisen in trying to understand how and why black holes behave as thermodynamic objects, having a temperature proportional to Planck's constant, and therefore by the first law an entropy inversely proportional to it. Hawking's calculation of the black hole blackbody spectrum raises further issues about how locality and causality can be consistent with quantum mechanical unitarity. After briefly reviewing these properties, I will present an overview of how string theory is answering these challenges using exotic phases of matter only available in a theory of extended objects inhabiting extra dimensions of space, and the additional topological complexity such geometries afford.

Dec
3
Wed 12:15
Susan Coppersmith, University of Wisconsin
e-mail:
Host: Leo Kadanoff ()
Compressed optimization of device architectures

Recent advances in nanotechnology have enabled researchers to control individual quantum mechanical objects with unprecedented accuracy, opening the door for both quantum and extreme-scale conventional computing applications. As these devices become larger and more complex, the ability to design them for simple control becomes a daunting and computationally infeasible task. Here, motivated by ideas from compressed sensing [1,2], we introduce a protocol for Compressed Optimization of Device Architectures (CODA) [3]. It leads naturally to a metric for benchmarking device performance and optimizing device designs, and provides a scheme for automating the control of gate operations and reducing their complexity. Because CODA is both experimentally and computationally efficient, it is readily extensible to large systems. We demonstrate the CODA benchmarking and optimization protocols through simulations of up to eight quantum dots in devices that are currently being developed experimentally for quantum computation.

[1] E. J. Candès, J. K. Romberg, and T. Tao, Communications on Pure and Applied Mathematics, 59, 1207 (2006) [2] D. Donoho, IEEE Transactions on Information Theory, 52, 1289 (2006) [3] A. Frees et al., arXiv:1409.3846

Dec
10
Wed 12:15
Igor Aronson, Argonne
e-mail:
Host: Leo Kadanoff ()
Jan 2015
7
Wed 12:15
Henry Cohn, Microsoft
e-mail:
Host: Leo Kadanoff ()
Jan 2015
14
Wed 12:15
Osvanny Ramos, University Claude Bernard Lyon 1
e-mail:
Host: Heinrich Jaeger
Jan 2015
21
Wed 12:15
OPEN
Jan 2015
28
Wed 12:15
Seth Lloyd, MIT
e-mail:
Host: Leo Kadanoff ()
Feb 2015
4
Wed 12:15
Zheng-Tian Lu, Argonne
Host: Daniel Holz ()
Feb 2015
11
Wed 12:15
OPEN
Feb 2015
18
Wed 12:15
Heinrich Jaeger, University of Chicago
e-mail:
Host: Leo Kadanoff ()
Feb 2015
25
Wed 12:15
OPEN
Mar 2015
4
Wed 12:15
OPEN
Mar 2015
11
Wed 12:15
OPEN
Mar 2015
18
Wed 12:15
OPEN
Mar 2015
25
Wed 12:15
OPEN
Apr 2015
1
Wed 12:15
Andrea Bertozzi, UCLA
e-mail:
Host: Leo Kadanoff ()
Apr 2015
8
Wed 12:15
Michael Brenner, Harvard
e-mail:
Host: Leo Kadanoff ()
Apr 2015
15
Wed 12:15
Michael Brenner, Harvard
e-mail:
Host: Leo Kadanoff ()
Apr 2015
22
Wed 12:15
Joseph Vallino, Marine Biological Labortory
e-mail:
Host: Leo Kadanoff ()
Apr 2015
29
Wed 12:15
Michael Rubenstein, Harvard
e-mail:
Host: Leo Kadanoff ()
May 2015
6
Wed 12:15
Tim Sanchez, Harvard
e-mail:
Host: Leo Kadanoff ()
May 2015
13
Wed 12:15
OPEN
May 2015
20
Wed 12:15
OPEN
May 2015
27
Wed 12:15
OPEN
Jun 2015
3
Wed 12:15
Alisa Bokulich, Boston University
e-mail:
Host: Leo Kadanoff ()
Jun 2015
10
Wed 12:15
OPEN
Jun 2015
17
Wed 12:15
OPEN
Jun 2015
24
Wed 12:15
OPEN