Glass Transition Phenomenon for Conjugated Polymers

Conjugated polymers are emerging as promising building blocks for a broad range of modern applications including skin‐like electronics, wearable optoelectronics, and sensory technologies. In the past three decades, the optical and electronic properties of conjugated polymers have been extensively studied, while their thermomechanical properties, especially the glass transition phenomenon which fundamentally represents the polymer chain dynamics, have received much less attention. Currently, there is a lack of design rules that underpin the glass transition temperature of these semirigid conjugated polymers, putting a constraint on the rational polymer design for flexible stretchable devices and stable polymer glass that is needed for the devices’ long‐term morphology stability. In this review article, the glass transition phenomenon for polymers, glass transition theories, and characterization techniques are first discussed. Then previous studies on the glass transition phenomenon of conjugated polymers are reviewed and a few empirical design rules are proposed to fine‐tune the glass transition temperature for conjugated polymers. The review paper is finished with perspectives on future directions on studying the glass transition phenomena of conjugated polymers. The goal of this perspective is to draw attention to challenges and opportunities of controlling, predicting, and designing polymeric semiconductors, specifically to accommodate their end use

The Influence of Channel Deepening on Tides, River Discharge Effects, and Storm Surge

We combine archival research, semi-analytical models, and numerical simulations to address the following question: how do changes to channel geometry alter tidal properties and flood dynamics in a hyposynchronous, strongly frictional estuary with a landward decay in tidal amplitudes? Records in the Saint Johns River Estuary since the 1890s show that tidal range has doubled in Jacksonville, Florida. Near the estuary inlet, tidal discharge approximately doubled but tidal amplitudes increased only ~6%. Modeling shows that increased shipping channel depths from 5-6 to ~13m drove the observed changes, with other factors like channel shortening and width reduction producing comparatively minor effects. Tidal amplitude increases are spatially variable, with a maximum change 20-25 km from the estuary inlet; tidal theory suggests that increases in amplitude approximately follow , where x is the distance from the ocean and is a damping coefficient. Tidal changes are a predictor of altered surge dynamics: Numerical modeling of hurricane Irma under 1898 and 2017 bathymetric conditions confirms that both tidal and storm surge amplitudes are larger today, with a similar spatial pattern. Nonetheless, peak water levels are simulated to be larger under 1898 bathymetry. The cause is likely the record river discharge observed during the storm; as suggested by a subtidal water-level model, channel deepening since 1898 appears to have reduced the average surface slope required to drain both mean river flow and storm flows towards the ocean. Nonetheless, results suggest an increased vulnerability to storms with less river flow, but larger storm surge

Park: An open platform for learning-augmented computer systems

© 2019 Neural information processing systems foundation. All rights reserved. We present Park, a platform for researchers to experiment with Reinforcement Learning (RL) for computer systems. Using RL for improving the performance of systems has a lot of potential, but is also in many ways very different from, for example, using RL for games. Thus, in this work we first discuss the unique challenges RL for systems has, and then propose Park an open extensible platform, which makes it easier for ML researchers to work on systems problems. Currently, Park consists of 12 real world system-centric optimization problems with one common easy to use interface. Finally, we present the performance of existing RL approaches over those 12 problems and outline potential areas of future work