Identification with Imperfect Instruments

Dealing with endogenous regressors is a central challenge of applied research. The standard solution is to use instrumental variables that are assumed to be uncorrelated with unobservables. We instead assume (i) the correlation between the instrument and the error term has the same sign as the correlation between the endogenous regressor and the error term, and (ii) that the instrument is less correlated with the error term than is the endogenous regressor. Using these assumptions, we derive analytic bounds for the parameters. We demonstrate the method in two applications

Non-Singular Black Holes in Massive Gravity: Time-Dependent Solutions

When starting with a static, spherically-symmetric ansatz, there are two types of black hole solutions in dRGT massive gravity: (i) exact Schwarzschild solutions which exhibit no Yukawa suppression at large distances and (ii) solutions in which the dynamical metric and the reference metric are simultaneously diagonal and which inevitably exhibit coordinate-invariant singularities at the horizon. In this work we investigate the possibility of black hole solutions which can accommodate both a non-singular horizon and Yukawa asymptotics. In particular, by adopting a time-dependent ansatz, we derive perturbative analytic solutions which possess non-singular horizons. These black hole solutions are indistinguishable from Schwarzschild black holes in the limit of zero graviton mass. At finite graviton mass, they depend explicitly on time. However, we demonstrate that the location of the apparent horizon is not necessarily time-dependent, indicating that these black holes are not necessarily accreting or evaporating (classically). In deriving these results, we also review and extend known results about static black hole solutions in massive gravity.Comment: 19 pages, 2 figure

Effect of Expansion and Magnetic Field Configuration on Mass Entrainment of Jets

We investigate the growth of jet plus entrained mass in simulations of supermagnetosonic cylindrical and expanding jets. The entrained mass spatially grows in three stages: from an initially slow spatial rate to a faster rate and finally at a flatter rate. These stages roughly coincide with the similar rates of expansion in simulated radio intensity maps, and also appear related to the growth of the Kelvin-Helmholtz instability through linear, nonlinear, and saturated regimes. In the supermagnetosonic cylindrical jets, we found that a jet with an embedded primarily toroidal magnetic field is more stable than a jet with a primarily axial magnetic field. Also, pressure-matched expanding jets are more stable and entrain less mass than cylindrical jets with equivalent inlet conditions.Comment: to appear in Life Cycles of Radio Galaxies, ed. J. Biretta et al., New Astronomy Reviews; 6 pages, including 3 figure

Human Trafficking and Foreign Policy: An Introduction

[Excerpt] Human trafficking (also known as trafficking in persons) refers to the subjection of men, women, or children to exploitative conditions that may be tantamount to modern-day slavery. From a foreign policy perspective, human trafficking can be viewed as a human rights problem, a manifestation of transnational organized crime, and a violation of core international labor standards. Human trafficking also raises economic development, international migration, and global governance and security issues, and disproportionately victimizes vulnerable populations. The Trafficking Victims Protection Act of 2000 (TVPA, Division A of P.L. 106-386; 22 U.S.C. 7101 et seq.) defined “severe forms of trafficking in persons” to include sex trafficking induced by force, fraud, or coercion, child sex trafficking (under 18 years of age), and forced labor trafficking. The latter involves the recruitment, harboring, transportation, provision, or obtaining of a person—induced by force, fraud, or coercion—for the purpose of subjecting that person, including a child, to involuntary servitude, peonage, debt bondage, or slavery