Hugoniot data for pyrrhotite and the Earth's core

New shock wave Hugoniot data for pyrrhotite (Fe_(0.9S)) now describe the equation of state to nearly twofold compression at a maximum pressure of 274 GPa. A minor discontinuity on the Hugoniot between 100 and 150 GPa is interpreted as the melting transition. While not tightly constrained, the inferred melting point lies below lower-bound temperature estimates based on the Lindemann criterion. The highest-pressure Hugoniot data (representing the melted phase) are used to model the equation of state for liquid iron sulfide. A density for liquid pyrrhotite of 7.80±0.20 Mg/m^3 under core-mantle boundary conditions (P = 135 GPa, T = 4000 K) is calculated. Assuming that sulfur is the primary alloying element in a predominately iron core, the present data are consistent with a homogeneous outer core containing 10±4 wt % sulfur

A Retrospective Analysis of the AT&T/Time Warner Merger

This article provides a retrospective of a litigated vertical merger: the 2018 AT&T/Time Warner merger, which was challenged by the US Department of Justice, litigated, and permitted to proceed by the court. We describe and evaluate in detail the economic model used by the government’s expert and then focus our empirical work on the accuracy of the predictions made by that model. We also discuss evidence related to the Comcast/NBC Universal merger, which involved the same theory of harm and was allowed to proceed with a remedy similar to the contractual commitment that AT&T/Time Warner unilaterally adopted. We conclude that the evidence from the time of trial showed the theory of harm to be weak and the specific empirical predictions made by the government’s expert to be wrong. Postmerger evidence confirms that conclusion, as does new evidence from the earlier Comcast/NBC Universal merger

A Retrospective Analysis of the AT&T/Time Warner Merger

This article provides a retrospective of a litigated vertical merger: the 2018 AT&T/Time Warner merger, which was challenged by the US Department of Justice, litigated, and permitted to proceed by the court. We describe and evaluate in detail the economic model used by the government’s expert and then focus our empirical work on the accuracy of the predictions made by that model. We also discuss evidence related to the Comcast/NBC Universal merger, which involved the same theory of harm and was allowed to proceed with a remedy similar to the contractual commitment that AT&T/Time Warner unilaterally adopted. We conclude that the evidence from the time of trial showed the theory of harm to be weak and the specific empirical predictions made by the government’s expert to be wrong. Postmerger evidence confirms that conclusion, as does new evidence from the earlier Comcast/NBC Universal merger

Modeling heart rate regulation - Part I:Sit-to-stand versus Head-up tilt

In this study we describe a model predicting heart rate regulation during postural change from sitting to standing and during head-up tilt in five healthy elderly adults. The model uses blood pressure as an input to predict baroreflex firing-rate, which in turn is used to predict efferent parasympathetic and sympathetic outflows. The model also includes the combined effects of vestibular and central command stimulation of muscle sympathetic nerve activity, which is increased at the onset of postural change. Concentrations of acetylcholine and noradrenaline, predicted as functions of sympathetic and parasympathetic outflow, are then used to estimate the heart rate response. Dynamics of the heart rate and the baroreflex firing rate are modeled using a system of coupled ordinary delay differential equations with 17 parameters. We have derived sensitivity equations and ranked sensitivities of all parameters with respect to all state variables in our model. Using this model we show that during head-up tilt, the baseline firing-rate is larger than during sit-to-stand and that the combined effect of vestibular and central command stimulation of muscle sympathetic nerve activity is less pronounced during head-up tilt than during sit-to-stand