### Links to Colloquia

Eisenbud Lecture Series in Mathematics and Physics

*All colloquium videos are under copyright and may not be reproduced, in part or in total, without written permission of the speaker and of the Physics Department.
*

## Department Colloquia

**Martin Weiner Lecture Series
Department of Physics Colloquium
4:00 pm, Abelson 131
Refreshments at 3:30pm outside Abelson 131**

**Fall 2016 Colloquia**

**Tuesday , September 6, 2016**

Aparna Baskaran (Brandeis)

*Active Materials : Applying the soft materials paradigm to Biology
* Host: Department of Physics

Abstract: In this talk I will introduce and discuss a recently developed class of microscopically driven materials that have been termed active materials. Drawing lessons from both biology and in vitro experimental systems, I will discuss theoretical challenges and different approaches that have proved fruitful so far. In particular, I will discuss the physics of active brownian particles and active nematics.

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**Tuesday, September 13, 2016**

Albion Lawrence (Brandeis)

*Cosmic inflation and quantum gravity
* Host: Department of Physics

Abstract: A new generation of cosmic microwave background (CMB) experiments are poised to test "high scale” models of cosmic inflation which are highly sensitive to quantum gravitational effects. In this talk I will review basic aspects of inflation and its imprint on the CMB, and then discuss the difficulties in constructing high-scale models which are not spoiled by quantum gravity. I will describe a specific class of models which use nontrivial quantum field theory dynamics to evade these difficulties.

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**Tuesday, September 20, 2016**

Chandralekha Singh (University of Pittsburgh)

*Improving student understanding of quantum mechanics *

Host: Prof. Matthew Headrick

Abstract: Learning quantum mechanics is challenging, in part due to the non-intuitive nature of the subject matter. Our research shows that the patterns of reasoning difficulties in learning quantum mechanics are often universal similar to the universal nature of reasoning difficulties found in introductory physics. Our research also shows that students often have difficulty in monitoring their learning while learning quantum mechanics. To help improve student understanding of quantum concepts, we are developing quantum interactive learning tutorials (QuILTs) as well as tools for peer-instruction. The goal of QuILTs and peer-instruction tools is to actively engage students in the learning process and to help them build links between the formalism and the conceptual aspects of quantum physics without compromising the technical content. I will discuss the effectiveness of these learning tools based upon assessment data.

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**Tuesday, September 27, 2016
** Ming Guo (MIT)

Title:

*The impact of cell volume and molecular crowding on cell mechanics and gene expression*

Host: W. Benjamin Rogers

Abstract: Cells alter their mechanical properties in response to their local microenvironment; this plays a role in determining cell function and can even influence stem cell fate. In this talk, I will show a robust and unified relationship between cell stiffness and cell volume. As a cell spreads on a substrate, its volume decreases while its stiffness concomitantly increases. The reduction of cell volume is a result of water efflux which leads to a corresponding increase in intracellular molecular crowding. We find that bulk modulus, cortical shear modulus and cytoplasmic shear modulus of cells all scale with cell volume, and possibly reflect the change in molecular crowding. Moreover, we have directly measured the equation of state of living mammalian cells, and find that it can be described by a hard-sphere equation of state. Finally, we find that changes in cell volume and hence stiffness alter stem-cell differentiation, regardless of the method by which these are induced. These observations reveal a surprising, previously unidentified, relationship between cell stiffness and cell volume which strongly influences cell biology, and highlight the impact of molecular crowding.

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**Tuesday, October 4, 2016**

No colloquium (Rosh Hashanah).

**Tuesday, October 11, 2016**

Irmgard Bischofberger, (MIT)

*Fingers, toes and tongues: the anatomy of interfacial instabilities in viscous fluids*

Host: W. Benjamin Rogers

Abstract: The invasion of one fluid into another of higher viscosity is unstable and produces complex patterns in a quasi-two dimensional geometry. This viscous-fingering instability, a bedrock of our understanding of pattern formation, has been characterized by a most-unstable wavelength that sets the characteristic width of the fingers. We have shown that a second, previously overlooked, parameter governs the length of the fingers and characterizes the dominant global features of the patterns.Because interfacial tension suppresses short-wavelength fluctuations, its elimination would suggest an instability producing highly ramified singular structures. Our experimental investigations using miscible fluids show the opposite behavior – the interface becomes more stable even as the stabilizing effect of interfacial tension is removed. This is accompanied by slender structures, tongues, that form in the narrow thickness of the fluid. Among the rich variety of global patterns that emerge is a regime of blunt structures, “toes”, that exhibit the unusual features characteristic of proportionate growth. This type of pattern formation, while quite common in mammalian biology, was hitherto unknown in physical systems.

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Daniel Gottesman (Perimeter Institute)

*Fault-tolerant quantum computation in the 21st century
* Host: Matthew Headrick

*Abstract:Experimentalists are getting better and better at building qubits, but no matter how hard they try, their qubits will never be perfect. In order to build a large quantum computer, we will almost certainly need to encode the qubits using quantum error-correcting codes and encode the quantum circuits using fault-tolerant protocols. This will eventually allow reliable quantum computation even when the individual components are imperfect. I will review the current state of the art of quantum fault tolerance and discuss progress towards answering the most important questions that will enable large fault-tolerant quantum computers.*

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**Tuesday, October 25, 2016**

No colloquium (Brandeis Monday).

Christopher Laumann (Boston University)

*Localization: Moving Beyond Statistical Mechanics*

Host: Albion Lawrence

Abstract: The central assumption of statistical mechanics is that interactions between particles establish local equilibrium. Isolated quantum systems, however, need not equilibrate; this happens, for example, when sufficient quenched disorder causes localization. The many-body localized (MBL) phase transports neither heat nor charge; may possess orders disallowed in equilibrium; and, may exhibit quantum coherence even when highly excited. We will review the emerging understanding of how quantum localization can lead to new quantum phenomena even in highly excited states. I will give some theoretical intuition about how this might be used to build a better quantum computer and also review some of the latest experiments investigating localization.

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Jeffrey Morris (CUNY)

Joint IGERT/Physics Department Colloquium

*Friction and adhesion in colloids: Yielding, thickening, jamming*

Host: Bulbul Chakraborty

Abstract: In recent work, we have shown [1,2] that frictional interactions provide a rational basis for both continuous and discontinuous shear thickening in viscous suspensions. When the repulsive forces (such as those due to electrostatic or steric colloidal stabilization) are overwhelmed by shearing forces, contact is assumed to occur, and the system transitions from a low-viscosity (lubricated) to a high-viscosity (frictional) state. Contacting particles may experience both adhesive forces as well as friction. We will consider the influence of attractive forces at contact, in combination with the stabilizing repulsive forces. This combination of forces would be seen in the case of particles with van der Waals attraction in combination with colloidal stabilization. For sufficient attractive force a yield stress and shear thinning give way to the shear thickening response, a behavior observed in certain flocculated dispersions. At sufficient yield stress, the shear thickening is completely obscured, as the dispersions shear thins after yielding directly onto the high-viscosity (frictional) plateau. The suggestion that a material may exhibit both yielding at low stress and jamming at large stress [3] is explored.

1. R. Seto, R. Mari**,** J. F. Morris & M. M. Denn 2013 Discontinuous shear thickening of frictional hard-sphere suspensions. *Phys. Rev. Lett. 111 218301.
2. . R. Mari, R. Seto J. F. Morris & M. M. Denn 2015 Discontinuous shear thickening in Brownian suspensions by dynamic simulation. Proc. National Acad. Sci.* 112. 15326.

3. N. J. Wagner & J. F. Brady 2009 Shear thickening in colloidal dispersions. Phys. Today62, 27-32.

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**Tuesday, November 15, 2016**

Time: 4:00pm

Location: Abelson 131

Eisenbud Lecture Series in Mathematics and Physics

Nigel Hitchin (Univ. of Oxford)

*Algebraic curves and differential equations*

Abstract: Euler’s equations for a spinning top are well-known to be solvable by elliptic functions. They form the first example of a much wider range of equations, in particular Nahm’s equations, which are solvable using algebraic curves of higher genus. Nahm’s equations appear in various parts of differential geometry and physics, related to hyperk ahler geometry and magnetic monopoles in particular. Loosely speaking, the equations are linearized on the Jacobian of the curve. However, there are many situations where that curve is singular or non-reduced and this viewpoint is no longer valid. The talk will discuss the geometry of what happens in some of these cases.

**Wednesday, November 16, 2016 (Lecture II)
** Time: 4pm

Location: Abelson 131

Eisenbud Lecture Series in Mathematics and Physics, Lecture II

Nigel Hitchin (Univ. of Oxford)

*Generalizing hyperbolic surfaces*

Abstract: The theory of Higgs bundles on a compact Riemann surface provided a natural setting for hyperbolic surfaces within the context of an SU(2)-gauge theory with a complex Higgs field. Replacing the group SU(2) by the group of symplectic diffeomorphisms of the two-sphere provides, thanks to work of Biquard, an infinite-dimensional gen eralization of Teichm ̈uller space, but it is as yet unclear what type of geometry, generalizing hyperbolic metrics, on the surface this parametrizes. The lecture will investigate some of the questions and features involved.

**Friday, November 18 (Lecture III)
** Time: 11:00am

Location: Abelson 126

Eisenbud Lecture Series in Mathematics and Physics, Lecture III

Nigel Hitchin (Univ. of Oxford)

*Higgs bundles and mirror symmetry*

Abstract: The moduli space of Higgs bundles on a curve, together with its fibration structure as an integrable system, forms a natural example to examine the predictions of mirror symmetry in the approach of Strominger, Yau and Zaslow. The mirror for gauge group G is regarded as being the moduli space for the Langlands dual group LG. Of particular interest is the how this manifests itself in the duality of “branes” on each side. We consider in the talk cases arising from noncompact real forms of complex groups, and also Lagrangians arising from the existence of holomorphic spinor fields.

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**Tuesday, November 22, 2016**

No colloquium (Thanksgiving week).

Raffaele Ferrari (MIT)

*The Physics of the Deep Ocean Circulation*

Host: Albion Lawrence

Abstract: The deep ocean circulation is fed by waters that become dense enough to sink into the ocean abyss at high latitudes and return to the surface through convoluted three dimensional pathways. While the physics behind the sinking of dense waters is well understood, the physics that allows waters to rise back to the surface remains elusive. It is generally believed that small-scale turbulent mixing, such as is caused by breaking internal waves, drives upwelling of the densest ocean waters. However the observational evidence that the turbulent fluxes generated by small-scale turbulent mixing in the stratified ocean interior are more vigorous close to the ocean bottom than above implies that small-scale turbulent mixing converts light waters into denser ones, thus driving a net sinking of abyssal water. Using a combination of numerical models and observations, it will be shown that abyssal waters return to the surface along weakly stratified boundary layers, where the small-scale turbulent mixing of density decays to zero. The net ocean meridional overturning circulation is thus the small residual of a large sinking of waters, driven by small-scale turbulent mixing in the stratified interior, and a comparably large upwelling, driven by the reduced small-scale turbulent mixing along the ocean boundaries.

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**Tuesday, December 6, 2016**

Chris Santangelo (UMass Amherst)

*Shape From Mechanics: Designing and Understanding Self-Folding Origami*

Host: W. Benjamin Rogers

Abstract: Origami, the ancient art of paper folding, has probably been around as long as paper. Yet, recent advances in materials have enabled the fabrication of self-folding origami structures, sometimes called “4d printing.” These self-folding structures promise to revolutionize the manufacture of complex structures on a variety of scales, yet realizing this has proven challenging. He will discuss recent work with collaborators on self-folding origami structures, focusing on the theory behind the mechanics of such structures, our limited understanding of how to design shape, and prospects for self-folding and responsive structures.

**Spring 2017 Colloquia**

**Tuesday, January 17, 2017**

Reserved.

**Tuesday, January 24, 2017**

Reserved.

**Tuesday, January 31, 2017**

Reserved.

**Tuesday, February 7, 2017
**

Reserved.

**Tuesday, February 14, 2017**

Reserved.

**Tuesday, February 21, 2017**

No colloquium. Midterm Recess.

**Tuesday, February 28, 2017**

Reserved.

**Tuesday, March 7, 2017**

David Keith (Harvard)

TBA

Host: W. Benjamin Rogers

**Tuesday, March 14, 2017**

No colloquium (APS).

**Tuesday, March 21, 2017**

John Bush (MIT)

TBA

Host: W. Benjamin Rogers

**Tuesday, March 28, 2017**

Steve Harvey (U Penn)

Joint Quantitative Biology/Department of Physics Colloquium

Host: Michael Hagan

**Tuesday, April 4, 2017**

Open.

**Tuesday April 11, 2017 **

No colloquium. Passover and spring recess.

**Tuesday, April 18, 2017**

No colloquium. Passover and spring recess.

**Tuesday, April 25, 2017**

James Battat (Wellesley)

TBA

Host: Gabriella Sciolla

**Tuesday, May 2, 2017**

Carl Haber (Lawrence Berkeley National Laboratory)

*Seeing Voices: Optical Scanning Applied to Early Recorded Sound Preservation*

Host: Gabriella Sciolla