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Colloquium: Eklund Student Lectures

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Aruna Kesavan, and Mark DelloStritto, Pennsylvania State University
When
28 January 2016 from 4:00 PM to 5:00 PM
Where
117 Osmond Laboratory
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Quantum mechanics of the universe: An origin story

Aruna Kesavan, Pennsylvania State University

The theory of inflation provides a remarkable account of how quantum fluctuations of fields in the very early universe serve as seeds for large scale structures observed in the universe. Despite its observational success, there is an important conceptual gap - How do quantum fluctuations generate the observed anisotropies in the Cosmic Microwave background (CMB) radiation, which are well-described by a classical probability distribution? I will illustrate the main issues, and describe some previous approaches to address them. I will then present geometric arguments and quantitative results showing that the accelerated expansion of the universe during inflation creates a squeezed vacuum state which leads to the emergence of classical behavior. Work presented here is done jointly with Abhay Ashtekar and Alejandro Corichi.

 

H-Bond Dynamics at Interfaces: A New Method for Nonlinear Optical Spectroscopy Calculations

Mark Dellostritto, Pennsylvania State University

Water/oxide interfaces are ubiquitous in the Earth’s crust, which is composed primarily of oxide minerals, and so are of basic importance in geochemistry and environmental science.  These interfaces are difficult to model however, as their behavior is dominated by H-bond interactions.  The H-bond network of water and its interaction with the oxide surface determines many surface properties, such as reaction rates, surface charge, and dissolution rates, and is highly sensitive to environmental perturbations, such as changes in temperature, pH, and ion concentration.  Studying the interfacial H-bond network is challenging due to the low symmetry of the system and the low charge and fast dynamics of the H atom.  The best method currently available is Sum Frequency Generation (SFG), a surface-specific nonlinear optical spectroscopy technique which is sensitive to dipole fluctuations at the interface.  By studying the high-frequency region of the vibrational spectrum obtained by SFG, one can find the vibrational resonances of the O-H bonds.  The structure and dynamics of the H-bond network can then be inferred from the direct relationship between the O-H vibrational frequencies and the H-bond length.  Although others have been able to calculate the SFG spectrum, they have been able to do so only for either crystalline materials or molecules in solution.  We present a method utilizing isotropic atomic polarizabilities in molecular dynamics simulations to treat both molecules, surfaces, and the interactions between them.  We are then able to decompose the spectrum in terms of microscopic molecular motions.  We test our method on the Al2O3(0001)-H2O interface and show good agreement with the vibrational spectrum obtained from SFG experiments.  

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