The 17th Amendment to the U.S. Constitution, ratified in 1913, introduced direct elections for the U.S. Senate, substantially democratizing the existing system of indirect selection by U.S. state legislatures. This paper analyzes the impacts of this reform on measures of each senator’s policy priorities constructed from the texts of their floor speeches and records of roll call votes. Using a difference-in-differences strategy comparing ...

Seismic traveltime tomography represents a popular and useful tool for unravelling the structure of the subsurface across the scales. In this work we address the case where the forward model is represented by the eikonal equation and derive a formalism to solve the inverse problem where gradients are calculated efficiently using the discrete adjoint state method. Our approach provides gradients with respect to both velocity structure and ...

We live in a time of highly accelerated extinction, which has the potential to mirror past mass extinction events. However, the rarity of these events and the restructuring of diversity that they cause complicate direct comparisons between the current extinction crisis and earlier mass extinctions. Among animals, turtles (Testudinata) are one of few groups which both have a sufficient fossil record and a sufficiently stable ecological ...