Northwestern University

Feb
13
Wed 12:00 PM

Brown Bag Lunch Seminar Series: Zhewei Yin and Travis Douglas

When: Wednesday, February 13, 2019
12:00 PM - 1:00 PM  

Where: Technological Institute, F160, 2145 Sheridan Road, Evanston, IL 60208 map it

Audience: Faculty/Staff - Student - Post Docs/Docs - Graduate Students

Contact: Bud Robinson   847.491.3644

Group: Physics and Astronomy Brown Bag Lunch Seminars

Category: Academic

Description:

Constructing Scattering Amplitudes of Nambu-Goldstone Bosons

Zhewei Yin

People have long been developing new ideas on formulating and calculating scattering amplitudes. I briefly discuss the motivation to go beyond the standard textbook formulation of Feynman diagrams, and then mainly focus on novel ways to construct amplitudes of a specific theory: the effective field theory of Nambu-Goldstone bosons. I review different ways to obtain the leading order interactions—the nonlinear sigma model, how soft theorems play a crucial part in it, and how new structures emerge in the soft limit of its amplitudes. I finally demonstrate recent development on how to extend the results to interactions sub-leading in the derivative expansion.

 

Cation-specific effects on the attraction of anions to a hydrophobic surface

Travis Douglas

Halides such as bromide and iodide are known to accumulate near the free surface of an electrolyte solution. Solid hydrophobic surfaces in contact with water induce a density-depleted gap near the interface, creating a water density profile similar to the free surface. It is therefore possible that polarizable ions like halides are also attracted to hydrophobic surfaces, a notion that is supported by MD simulations. However, the buried solid-liquid interface is more difficult to access experimentally than the free surface of water and is thus much less studied. I will present results of an x-ray reflectivity study of aqueous alkali metal-iodide solutions in contact with a hydrophobic self-assembled monolayer (SAM). A layer of enhanced anion density is observed at the SAM-water interface, but with an unexpected strong dependence on the cation present in the solution. This experiment attempts to provide insight into the less understood yet ubiquitous interactions between ions and real hydrophobic/non-polar materials, such as proteins and organic molecules present in the atmosphere and soil.

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