Interferometric differentiation between resonant Coherent Anti-Stokes Raman Scattering and nonresonant four-wave-mixing processes

A major impediment of using Coherent Anti-Stokes Raman Scattering to identify biological molecules is that the illumination levels required to produce a measurable signal often also produce significant nonresonant background from the medium, especially from water, that is not specific to the resonance being investigated. We present a method of using nonlinear interferometry to measure the temporal shape of the anti-Stokes signal to differentiate which components are resonant and nonresonant. This method is easily adaptable to most existing pulsed CARS illumination methods and should allow for distinguishing resonant CARS when using higher energy pulses. By examining the differences between signals produced by acetone and water, we show that the resonant and nonresonant signals can be clearly differentiated.Comment: 8 pages, 4 figure

Magnetically Tunable Feshbach Resonances in Ultracold Li-Yb Mixtures

We investigate the possibility of forming Li+Yb ultracold molecules by magnetoassociation in mixtures of ultracold atoms. We find that magnetically tunable Feshbach resonances exist, but are extremely narrow for even-mass ytterbium isotopes, which all have zero spin. For odd-mass Yb isotopes, however, there is a new mechanism due to hyperfine coupling between the electron spin and the Yb nuclear magnetic moment. This mechanism produces Feshbach resonances for fermionic Yb isotopes that can be more than 2 orders of magnitude larger than for the bosonic counterparts

Prospects of forming ultracold molecules in double-Sigma states by magnetoassociation of alkali-metal atoms with Yb

We explore the feasibility of producing ultracold diatomic molecules with nonzero electric and magnetic dipole moments by magnetically associating two atoms, one with zero electron spin and one with nonzero spin. Feshbach resonances arise through the dependence of the hyperfine coupling on internuclear distance.We survey the Feshbach resonances in diatomic systems combining the nine stable alkali-metal isotopes with those of Yb, focusing on the illustrative examples of RbYb and CsYb. We show that the resonance widths may expressed as a product of physically comprehensible terms in the framework of Fermi’s golden rule. The resonance widths depend strongly on the background scattering length, which may be adjusted by selecting the Yb isotope, and on the hyperfine coupling constant and the magnetic field. In favorable cases the resonances may be over 100 mG wide

A Parallel Solver for Graph Laplacians

Problems from graph drawing, spectral clustering, network flow and graph partitioning can all be expressed in terms of graph Laplacian matrices. There are a variety of practical approaches to solving these problems in serial. However, as problem sizes increase and single core speeds stagnate, parallelism is essential to solve such problems quickly. We present an unsmoothed aggregation multigrid method for solving graph Laplacians in a distributed memory setting. We introduce new parallel aggregation and low degree elimination algorithms targeted specifically at irregular degree graphs. These algorithms are expressed in terms of sparse matrix-vector products using generalized sum and product operations. This formulation is amenable to linear algebra using arbitrary distributions and allows us to operate on a 2D sparse matrix distribution, which is necessary for parallel scalability. Our solver outperforms the natural parallel extension of the current state of the art in an algorithmic comparison. We demonstrate scalability to 576 processes and graphs with up to 1.7 billion edges.Comment: PASC '18, Code: https://github.com/ligmg/ligm

Complementary Macroprudential Regulation of Nonbank Entities and Activities

In this blog entry, the authors describe their forthcoming law review article in Southern California Law Review

Comment of Legal Scholars on Authority To Require Supervision and Regulation of Certain Nonbank Financial Companies, Financial Stability Oversight Council RIN 4030-AA00

Professor McCoy coauthored this comment on a proposal by the Financial Stability Oversight Council to overhaul systemic risk regulation for nonbank financial firms

The Abacus Cosmos: A Suite of Cosmological N-body Simulations

We present a public data release of halo catalogs from a suite of 125 cosmological $N$-body simulations from the Abacus project. The simulations span 40 $w$CDM cosmologies centered on the Planck 2015 cosmology at two mass resolutions, $4\times 10^{10}\;h^{-1}M_\odot$ and $1\times 10^{10}\;h^{-1}M_\odot$, in $1.1\;h^{-1}\mathrm{Gpc}$ and $720\;h^{-1}\mathrm{Mpc}$ boxes, respectively. The boxes are phase-matched to suppress sample variance and isolate cosmology dependence. Additional volume is available via 16 boxes of fixed cosmology and varied phase; a few boxes of single-parameter excursions from Planck 2015 are also provided. Catalogs spanning $z=1.5$ to $0.1$ are available for friends-of-friends and Rockstar halo finders and include particle subsamples. All data products are available at https://lgarrison.github.io/AbacusCosmosComment: 13 pages, 9 figures, 3 tables. Additional figures added for mass resolution convergence tests, and additional redshifts added for existing tests. Matches ApJS accepted versio

Regulating Entities and Activities: Complementary Approaches to Nonbank Systemic Risk

The recent financial crisis demonstrated that, contrary to longstanding regulatory assumptions, nonbank financial firms—such as investment banks and insurance companies—can propagate systemic risk throughout the financial system. After the crisis, policymakers in the United States and abroad developed two different strategies for dealing with nonbank systemic risk. The first strategy seeks to regulate individual nonbank entities that officials designate as being potentially systemically important. The second approach targets financial activities that could create systemic risk, irrespective of the types of firms that engage in those transactions. In the last several years, domestic and international policymakers have come to view these two strategies as substitutes, largely abandoning entity-based designations in favor of activities-based approaches. This Article argues that this trend is deeply misguided because entity- and activities-based approaches are complementary tools that are each essential for effectively regulating nonbank systemic risk. Eliminating an entity-based approach to nonbank systemic risk—either formally or through onerous procedural requirements—would expose the financial system to the same risks that it experienced in 2008 as a result of distress at nonbanks like AIG, Bear Stearns, and Lehman Brothers. This conclusion is especially salient in the United States, where jurisdictional fragmentation undermines the capacity of financial regulators to implement an effective activities-based approach. Significant reforms to the U.S. regulatory framework are necessary, therefore, before an activities-based approach can meaningfully complement domestic entity-based systemic risk regulation