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September 17, 2018

The state of the department, the state of the department head, and the state of human vision

Date:  Thursday, September 27, 2018

Time: 4:00pm

Location: 100 Willamette Hall

Speaker:   Richard Taylor, Department Head, UO Physics

Abstract:

After three months with a new departmental head, I’m sure we are all curious to reflect on the current  ‘state’ of our department! In this talk, I will give you some qualitative and quantitative observations to help guide us in the year ahead. I’ve already written the first line: ”This is an exciting but complex time for our department.” If we have time, I will also talk about the state of human vision and the research done in this department to restore vision to those who have lost it.

Host:  Dietrich Belitz

All attendees are invited to attend a colloquium reception in the Willamette Hall, Paul Olum atrium at 3:40pm.

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June 8, 2018

The Physics colloquium series will resume fall term 2018

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June 1, 2018

Towards a physics of behavior: If Newton watched the worm, not the apple

Speaker: Greg Stephens, Vrije University and Okinawa Institute of Science and Technology)

Abstract:
We use the posture dynamics of the nematode C. elegans to explore whether we can be as precise about the laws and principles that govern the emergent scale of entire organisms as we are about the molecules, cells and circuits from which behavior is ultimately derived. We exploit ideas from dynamical systems and statistical physics to reconstruct the worm’s phase space directly from the movement time series. We show that the dynamics lie on a 6D manifold, composed of forward, backward and turning motions. In contrast to global stereotypy, local variability is evident in positive Lyapunov exponents for each behavior. Over the full phase space, positive, chaotic exponents driving variability are balanced by negative, dissipative exponents driving stereotypy and the dynamics exhibit a near-Hamiltonian symmetry. This symmetry holds for different environments and organisms suggesting a general condition of motor control.

Host: Caleb Holt

Date: Thursday, June 7th, 2018
Time: 4:00-5:00pm
Location: 100 Willamette Hall

Catered Reception: 3:40pm-3:55pm, Willamette Hall, Paul Olum Atrium

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May 25, 2018

Uncovering the Quantum Nature of Light

Speaker:  Werner Vogel, University of Rostock

Abstract:

We consider quantum properties of light, such as nonclassicality, entanglement, and general quantum correlations.  We start by introducing the notions of nonclassical and entangled quantum states and identify their origin in the quantum superposition principle. Some examples for experimental reconstructions of quantum states are given. Properties of nonclassical states are discussed with particular emphasis on squeezed states. We introduce a method to visualize the nonclassicality of such quantum states in experiments by direct sampling of a so-called nonclassicality quasiprobability. The verification of quantum entanglement is considered for complex multipartite scenarios. Our approach allows us to verify entanglement beyond the simple case of bipartitions. Finally we consider general, space-time-dependent quantum correlations of light. Our method uncovers quantum correlations even when other signatures of quantumness fail to do so.

Host: Brian Smith

Date:  Thursday, May 31st, 2018
Time: 4:00-5:00pm
Location: 100 Willamette Hall

Catered Reception: 3:40pm-3:55pm, Willamette Hall, Paul Olum Atrium

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May 21, 2018

Once Upon a Time in Kamchatka: The Extraordinary Search for Natural Quasicrystals

Speaker:  Paul Steinhardt, Princeton University

Abstract:

Quasicrystals are exotic materials with symmetries that were once thought to be impossible for matter.  The first known examples were synthesized in the laboratory over 30 years ago, but could Nature have beaten us to the punch?  This talk will describe the search that took over a dozen years to answer this question, resulting in one of the strangest scientific stories you are ever likely to hear.

Host: John Toner

Date:  Thursday, May 24th, 2018
Time: 4:00-5:00pm
Location: 100 Willamette Hall

Catered Reception: 3:40pm-3:55pm, Willamette Hall, Paul Olum Atrium

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May 11, 2018

May 17th Physics colloquium CANCELLED

Please be advised that the Thursday, May 17th Physics colloquium has been cancelled due to laryngitis.

 

 

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May 4, 2018

Re-Examining Astrophysical Constraints on the Dark Matter Model

Speaker:  Alyson Brooks, Rutgers University

Abstract:

The cosmological model based on cold dark matter (CDM) and dark energy has been hugely successful in describing the observed evolution and large scale structure of our Universe. However, at small scales (in the smallest galaxies and at the centers of larger galaxies), a number of observations seem to conflict with the predictions of CDM cosmology, leading to recent interest in alternative dark matter models. I will summarize a number of ways that including baryonic physics (the physics of gas and stars) can resolve the conflict between theory and observations, by significantly altering the structure and evolution of galaxies. Despite all of the successes of baryonic physics in reconciling CDM with observations, I will explain why alternative dark matter models are still viable and interesting.

Host: Graham Kribs

Date:  Thursday, May 10th, 2018
Time: 4:00-5:00pm
Location: 100 Willamette Hall

Catered Reception: 3:40pm-3:55pm, Willamette Hall, Paul Olum Atrium

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April 26, 2018

Fluids that Stiffen and Swim

Speaker:  Daniel Blair, Georgetown University

Abstract:

In this talk I will discuss our recent results on the microscopic physical origins of shear thickening in sheared colloidal suspensions and the viscoelasticity of active fluids. In the first part of my talk, I will introduce a method we have developed that allows us to resolve the spatial distribution of stresses in sheared soft-materials, known as Boundary Stress Microscopy. We have applied this technique suspensions undergoing continuous and discontinuous shear thickening. I will present our results on the existence of clearly defined dynamically localized regions of substantially increased stress that appear intermittently at stresses well above the applied stress. Surprisingly, we find that these spatially distinct and dynamic phases account quantitatively for the observed shear thickening seen in sheared colloidal dispersions (e.g. Oobleck). In the second part of my talk I will discuss our results on the rheology of active matter. Our system is composed of microtubules and motor kinesin proteins that self-assemble to form complexes that propel themselves through the fluid, resulting in spontaneous “swimming” of the suspended material. What results is an interplay between the internal active stresses and any imposed external stress. I will discuss the impact of the internal flows have on the local and bulk rheological response.

Host: Eric Corwin

Date:  Thursday, May 3rd, 2018
Time: 4:00-5:00pm
Location: 100 Willamette Hall

Catered Reception: 3:40pm-3:55pm, Willamette Hall, Paul Olum Atrium

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April 20, 2018

Quantum Mechanical Bounds on Transport from First Principles

Speaker:  Sean Hartnoll, Stanford University

Abstract:

Some of hardest theoretical challenges in strongly-interacting many-body systems are concerned with transport. This involves understanding quantities such as the electric resistivity, the thermal conductivity, the viscosity, spin diffusivity etc. of media as diverse as the quark-gluon plasma, unconventional metals and cold atomic gases. I will argue that a handle on these problems can be gained from understanding fundamental limits on the dynamics of many-body systems imposed by quantum mechanics and statistical mechanics themselves. The advantage of this approach is that it does not depend on the presence of weakly interacting quasiparticles.

Host: Tim Cohen

Date:  Thursday, April 26th, 2018
Time: 4:00-5:00pm
Location: 100 Willamette Hall

Catered Reception: 3:40pm-3:55pm, Willamette Hall, Paul Olum Atrium

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April 13, 2018

Why Systems Biology Shouldn’t Work but Does and What Heat Capacity Can Explain About Inference

Speaker:  Paul Wiggins, University of Washington

Abstract:

Why do systems biology models work in spite of a blizzard of poorly-defined parameters and yet the detection of the Higgs boson required five sigma precision? Scientific and technological innovations are rapidly increasing the size and scope of datasets. Accompanying this growth come new challenges in analysis, interpretation and modeling. Fundamental questions remain about the mechanism of learning. To study the universal principles governing these processes, we expand upon a long-discussed correspondence between thermodynamics and statistics. This correspondence to thermal physics provides some surprising insights into the mechanism of learning. An analogy to heat capacity demonstrates both a universal scaling of learning algorithms as well as how and why these scaling relations fail in many of the most interesting models, including systems biology models. An analogy to the Gibbs entropy provides a new algorithm for efficient inference, well-suited to single-molecule-fluorescence measurements where the number of photons collected is small.

Host: Tristan Ursell

Date:  Thursday, April 19th, 2018
Time: 4:00-5:00pm
Location: 100 Willamette Hall

Catered Reception: 3:40pm-3:55pm, Willamette Hall, Paul Olum Atrium

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