Computations in Science Seminars
Aug
6
Wed 12:15
Andrew Gronewold, Great Lakes Environmental Research Laboratory
e-mail:
Host: Leo Kadanoff ()
Drivers of water level change on Earth’s largest lake system

In December 2012 and January 2013, water levels on Lake Michigan-Huron (the single largest area of fresh surface water on Earth) dropped to record lows (based on a record dating to the mid-1800s). This hydrological event occurred during a period (that begin in the late 1990s) in which the North American Great Lakes have been characterized by above average water temperatures, high evaporation rates, and persistent low water levels. Recent research suggests, however, that the extreme cold winter of 2013-2014 may have significantly lowered the heat content of the Great Lakes, and could signify a transition between hydrological and thermal regimes.

Here, I explore historical drivers of water level change across the Great Lakes, with a particular emphasis on analyzing model simulations and forecasts that propagate changes in regional precipitation, temperature, and evaporation into seasonal and interannual water budget and level dynamics. I assess the skill of these models, and underscore periods when they have performed well, and when they have failed to adequately explain observed water level variability. I conclude with a discussion of water level projections, and the scientific research needed to improve their skill over different time scales.

Aug
7
Thu 12:15
Jean-Pierre Delville, University of Bordeaux
e-mail:
Host: Wendy Zhang ()
Pinching Dynamic and Breakup of Fluctuating Liquid Columns
Special day: Thursday August 7

The droplet formation and production from liquid jets and columns are very familiar and important in every day’s life. The pinching dynamics of liquid thread follows well established laws depending on inertia, viscous effects and capillary forces. However, before breakup, pinched necks reach nanometric dimensions comparable to the scale of ambient thermal fluctuations; this new length scale may play a role in the ultimate pinch-off stage. If in “classical” situations, this thermal regime has no influence on the drop production, the device miniaturization and the increasing use of fluids in nanotechnologies should alert us with example such as flows in nanotubes or thermal annealing of nanowires where the length scale may compare to the thermal length. New rupture mechanisms and then different droplet distributions are expected. Their investigation remains nonetheless a real challenge. A route for investigating this fluctuation-dominated regime consists in using near-critical phase-separated fluids as the amplitude of fluctuations can be tuned with the proximity to the critical point. After an introduction to the dynamic of breakup in the viscous and thermal fluctuation regime, we will illustrate the universal character of these two regimes in near-critical phases of micro-emulsions and demonstrate the existence of a well-defined crossover between them when the neck radius reaches the thermal length. Moreover, we show that the neck morphology becomes symmetric in the thermal fluctuation regime, thus leading to the disappearance of satellite drops and to the production of monodisperse droplets. Finally, we present some further preliminary results on the dynamics of liquid ligaments and nanojet analogs when fluctuations are important.

Aug
13
Wed 12:15 PM
William A. Dembski, Discovery Institue
e-mail:
Conservation of Information in Evolutionary Search

Conservation of Information (CoI) asserts that the amount of information a search outputs can equal but never exceed the amount of information it inputs. Mathematically, CoI sets limits on the information cost incurred when the probability of success of a targeted search gets raised from p to q (p < q), that cost being calculated in terms of the probability p/q. CoI builds on the No Free Lunch (NFL) theorems, which showed that average performance of any search is no better than blind search. CoI shows that when, for a given problem, a search outperforms blind search, it does so by incorporating an amount of information determined by the increase in probability with which the search outperforms blind search. CoI applies to evolutionary search, showing that natural selection cannot create the information that enables evolution to be successful, but at best redistributes already existing information. CoI has implications for teleology in nature, consistent with natural teleological laws mooted in Thomas Nagel's Mind & Cosmos.

Aug
20
Wed 12:15
Glen Weyl, University of Chicago
e-mail:
Host: Leo Kadanoff ()

Democratic government is famously plagued by problems such as the tyranny of the majority and political paralysis. These result from fundamental flaws of one-man-one-vote as a mechanism for collective decisions identified by economists. A simple alternative procedure, Quadratic Voting (QV), solves these problems and offers a practical, efficient, simple and robust alternative. Individuals purchase votes using either money or an artificial currency that may be spread across multiple issues and pay the square of the number of votes purchased. QV is efficient because individuals optimally equate the marginal cost of a vote to the benefit they derive from an additional vote and thus set the number of votes purchased proportional to their values for the outcome if all individuals take the chance of their being pivotal in the outcome as approximately constant. This "should" be true in large populations and a number of detailed approximate calculations, intermediate analytic results and numerical simulations have persuaded us of this. However, we have as of yet been unable to rigorously prove the convergence results that we conjecture in detail due to the small probability of a single individual purchasing a large number of votes that turns out to be necessary to sustain equilibrium. After a brief introduction to the motivation, I plan to devote most of the talk to these formal difficulties in hopes of soliciting suggestions on how to clear these roadblocks.

Aug
27
Wed 12:15
Sayantan Majumdar, University of Chicago
e-mail:
Host: Leo Kadanoff ()
History dependent shear response in cross-linked actin networks

Is it possible to control the shear modulus of a material mechanically? We reconstitute an assembly of cross-linked actin filaments, a major component of cell cytoskeleton, to show that the system has remarkable property to respond under shear in a deformation history dependent manner. When a large shear stress pulse is applied to the system, the system remembers the direction of deformation long after the stress pulse is removed. For next loading cycle, shear response of the system becomes anisotropic; if the applied pulse direction is same as the previous one, the system behaves like a viscoelastic solid but a transient liquefaction is observed if the pulse direction is reversed with respect to the previous one. Further experiments suggest that this anisotropic response comes from stretching dominated and bending dominated deformation directions induced by the large shear deformation giving rise to a direction dependent mechano-memory. The long time scale over which the memory effect persists has relevance in various deformations in cellular and multicellular systems.

Oct
1
Wed 12:15
Stas Nagy, University of Chicago
Host: Leo Kadanoff ()
snagy@uchicago.edu
Oct
8
Wed 12:15
Bob Batterman, University of Pittsburgh
e-mail:
Host: Leo Kadanoff ()
Oct
15
Wed 12:15
Jane Wang, Cornell
e-mail:
Host: Leo Kadanoff ()
Oct
22
Wed 12:15
Andy Ruina, Cornell
e-mail:
Host: Leo Kadanoff ()
Oct
29
Wed 12:15
Kerry Emanuel, MIT
e-mail:
Host: Leo Kadanoff ()
Nov
5
Wed 12:15
Guenter Ahlers, UC Santa Barbara
e-mail:
Host: Leo Kadanoff ()
Nov
12
Wed 12:15
Luis Bettencourt, Santa Fe Institute
e-mail:
Host: Leo Kadanoff ()
Nov
19
Wed 12:15
Emil Martinec, University of Chicago
e-mail:
Dec
3
Wed 12:15
Susan Coppersmith, University of Wisconsin
e-mail:
Host: Leo Kadanoff ()
Dec
10
Wed 12:15
Igor Aronson, Argonne
e-mail:
Host: Leo Kadanoff ()
Jan 2015
7
Wed 12:15
OPEN
Jan 2015
14
Wed 12:15
OPEN
Jan 2015
21
Wed 12:15
Heinrich Jaeger, University of Chicago
e-mail:
Host: Leo Kadanoff ()
Jan 2015
28
Wed 12:15
Seth Lloyd, MIT
e-mail:
Host: Leo Kadanoff ()
Feb 2015
4
Wed 12:15
OPEN
Feb 2015
11
Wed 12:15
OPEN
Feb 2015
18
Wed 12:15
OPEN
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
OPEN
Apr 2015
15
Wed 12:15
OPEN
Apr 2015
22
Wed 12:15
OPEN
Apr 2015
29
Wed 12:15
OPEN
May 2015
6
Wed 12:15
OPEN
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
OPEN
Jun 2015
10
Wed 12:15
OPEN
Jun 2015
17
Wed 12:15
OPEN
Jun 2015
24
Wed 12:15
OPEN