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The nucleolus is a multicomponent structure made of RNA and proteins that serves as the site of ribosome biogenesis within the nucleus. It has been extensively studied as a prototype of a biomolecular condensate whose assembly is driven by phase separation. While the steady-state size of the nucleolus is quantitatively accounted for by the thermodynamics of phase separation, we show that experimental measurements of the assembly dynamics are inconsistent with a simple model of a phase-separating system relaxing to its equilibrium state. Instead, we show that the dynamics are well described by a model in which the transcription of ribosomal RNA actively drives nucleolar assembly. We find that our model of active transcription-templated assembly quantitatively accounts for the rapid kinetics observed in early embryos at different developmental stages, and for different RNA interference (RNAi) perturbations of embryo size. Our model predicts a scaling of the time to assembly with the volume of the nucleus to the one-third power, which is confirmed by experimental data. Our study highlights the role of active processes such as transcription in controlling the placement and timing of assembly of membraneless organelles. 

Electric vehicle (EV) sales have been rapidly growing around the world, spurred by technology advances and policy actions. This study leverages rich data on all individual new light-duty vehicles sold in the United States from 2014 to 2020. We examine how EV attributes, prices, and sales have evolved, exploring substantial heterogeneity across geography, vehicle class, price range, and demographics. We use a matching analysis to compare EVs to similar conventional vehicles to find that EVs have been surprisingly competitive in very recent years. This suggests that constrained supply is an important determinant of the low overall EV market share.