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February 10, 2014

February 13, 2014 Colloquium

G.D. Bothun, University of Oregon

Global Climate Change IS Increasing Weather Volatility

 For many people, climate change is perceived to manifest as a systematic shift away from average weather to some kind of new average weather.  A priori, there was never any physical reason to expect this kind of behavior; only glacial-interglacial dynamics produces these shifts.  As a consequence, denial of climate change is rising because there is no perception of an average weather change.    However, climate is a complex and non-linear interplay between the surface ocean heat distribution and the atmospheric heat distribution and the natural timescales in those systems is different by three orders of magnitude.   By adding energy (now measureable) to the atmospheric-ocean interface, humans have changed pathways and exchange rates, leading to a non-linear response of the system that is manifest as climate volatility.   This climate volatility easily now appears in the data.  Three most recent examples are a) two extreme polar vortex intrusions to very southerly latitudes, b) last summer’s incredibly weak jet stream that lead to prolonged retrograde storms (storms that move from east to west) and c) the conditions that spawned SuperStorm Sandy.    This talk will make the case that climate volatility is quite real, that some non-linear thresholds are being reached, that increases in deep tropical convection may be the principle driver of the currently observed volatility, and that the connections between the oceans and the atmosphere are deeper and more complicated that previously appreciated.    Most all of this has come to light within just the last 3-4 years due to significant advances in observational instrumentation and computational modeling and has re-written climate literacy 101.

  • REFRESHMENTS:  3:40 p.m. in the Willamette Atrium
  • COLLOQUIUM:   4:00 p.m. in Willamette 100
February 5, 2014

Thursday, February 6 Colloquium

Stefania Gori, Perimeter Institute of Theoretical Science

Beyond the Higgs boson discovery

Abstract: After almost five decades from its first theoretical proposal, the most wanted elementary particle, the Higgs boson, or something that closely looks like it, has finally been discovered by the Large Hadron Collider (LHC) at CERN. I will review the crucial role of this discovery for the self-consistency of the “Standard Model” of particle physics. I will discuss what we expect to learn from dedicated measurements of Higgs properties about fundamental physics that cannot be explained in the framework of the Standard Model.

  • REFRESHMENTS:  3:40 p.m. in the Willamette Atrium
  • COLLOQUIUM:   4:00 p.m. in Willamette 100
  • HOST:  Graham Kribs
February 3, 2014

February 4 Colloquium

Tristan Ursell, Stanford University

Growth and Shape Control in Bacteria

Abstract: In bacteria, a host of enzymes regulates the reproducible and robust construction of the cell wall, whose mechanical integrity is crucial for viability under osmotic stress. Antibiotics that target these enzymes disrupt cell wall construction, ultimately leading to mechanical failure of the cell. Our work explores the physical mechanisms of cell growth and death, as a guide to understanding antibiotic mechanisms that disrupt mechanical properties of the cell. We use a combination of cell wall fluorescent labeling, high resolution time-lapse microscopy, and computational image processing to characterize where, and with what dynamics, cell wall and outer membrane growth occurs. Analysis of cell-surface marker fluorescence indicates that the cytoskeleton is present at sites of active growth and that chemical depolymerization of the cytoskeleton causes homogeneous, unstructured growth and eventual cell death by rupture. When combined with cell-shape analysis, our data strongly suggest that dynamic localization of the bacterial cytoskeleton is part of a curvature sensing and growth feedback mechanism that orchestrates heterogeneous growth to maintain cell shape and regulate mechanical stress. Using surface-specific protein labeling, we show that outer membrane growth also occurs in a similar heterogeneous manner. Quantitative tracking of growth is an effective method for characterizing cell wall mechanical failure resulting from antibiotic treatment. These techniques pave the way for studying the detailed dynamics of growth-associated proteins and their disturbance by antibiotics.

Host: Raghuveer Parthasarathy

January 28, 2014

January 30 Colloquium

Kun Zhao, University of California, Los Angeles

From Colloids to Bacteria:Anisotropy in Self-Organizing Systems at the Mesoscopic Scale

Abstract:  Many complex mesoscopic systems, ranging from inorganic colloids to active biological cells, exhibit a rich variety of pattern-forming behavior. In this talk, I will show you how anisotropy in two model systems, anisotropic shaped colloids and bacterial communities, affect complex pattern formation. During the directed self-assembly of colloidal systems, shape anisotropy can greatly influence resulting structures. We have developed a technique called roughness controlled depletion attraction which allows us to probe the phase space of 2D Brownian systems for a variety of anisotropic shapes such as triangles, squares, and other polygons. We have discovered several unanticipated effects, such as local symmetry breaking in a triatic liquid crystal phase of uniform triangles. Anisotropy also plays a large role in the formation of bacterial communities called biofilms. Biofilms are a major human health hazard as well as being an impediment in many industrial and medical settings. By using condensed matter techniques, we present for the first time the dynamics of colony formation at early stages of biofilm development for Pseudomonas aeruginosa. We found that Pseudomonas aeruginosa does not follow an isotropic random walk as commonly assumed, but instead obeys a new form of polysaccharide-guided dynamics such that the distribution of surface.

Host: Raghuveer Parthasarathy

January 23, 2014

January 23 Colloquium

Liam Fitzpatrick, Stanford University

Effective Field Theory and the Emergence of New Dynamics

I describe applications of Effective Field Theory (EFT) to a broad range of scenarios where novel physics has been observed but the details remain poorly constrained. I discuss how EFT allows one to simplify and organize existing models, as well as providing an efficient framework for envisioning and parameterizing general possibilities in a more model-independent manner. Applications covered will be inflation in the early universe, experiments looking for direct detection of dark matter, and novel phases in superconducting metals.

January 16, 2014

January 16 Colloquium

Jay Wacker, SLAC National Laboratory

The Search For New Physics in the LHC Age

The first run of the LHC has just completed and the first set of analyses have just come out. I will review the state of searches for new physics at the LHC and give interpretations of the results. I will focus on the interplay between the discovery of the Higgs boson and the implications for supersymmetric extensions of the Standard Model.

January 9, 2014

January 9 Colloquium

Megan McClean, Princeton University

Elucidating Principles of Biological Signal Processing Using Microfluidic and Optogenetic Tools

Biological networks, like electrical circuits, take specific inputs (nutrient availability, stress, hormones) and convert them into appropriate outputs (transcriptional responses, metabolic remodeling). Electrical engineers uncover the inner workings of such circuits by measuring the transfer function between input voltage and output voltage. However, unlike electrical engineers, biologists are more limited in the input signals they can generate to interrogate such networks. We are developing microfluidic and optogenetic tools to generate dynamic inputs to interrogate and control natural and synthetic biological networks. In this talk I will discuss our use of microfluidics to dissect the mechanisms and kinetics of signaling in stress response networks in the budding yeast Saccharomyces cerevisiae. In addition, I will discuss our recent efforts to develop real-time optogenetic control of protein concentration as a tool for manipulating biological networks.

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