On the contribution of exchange interactions to the Vlasov equation

Exchange effects play an important role in determining the equilibrium properties of dense matter systems, as well as for magnetic phenomena. There exists an extensive literature concerning, e.g., the effects of exchange interactions on the equation of state of dense matter. Here, a generalization of the Vlasov equation to include exchange effects is presented allowing for electromagnetic mean fields, thus incorporating some of the dynamic effects due to the exchange interactions. Treating the exchange term perturbatively, the correction to classical Langmuir waves in plasmas is found, and the results are compared with previous work. It is noted that the relative importance of exchange effects scales similarly with density and temperature as particle dispersive effects, but that the overall magnitude is sensitive to the details of the specific problem. The implications of our results are discussed.Comment: 9 page

Regularizing velocity differences in time-lapse FWI using gradient mismatch information

We present a method for recovering time-lapse velocity changes using full waveform inversion (FWI). In a preprocessing step we invert for a single intermediate model by simultaneously minimizing the data misfit in the baseline and the monitor surveys. We record the individual FWI gradients corresponding to the baseline and the monitor datasets at each iteration of the inversion. Regions where these gradients consistently have opposing sign are likely to correspond to locations of time-lapse change. This insight is used to generate a spatially varying confidence map for time-lapse change. In a subsequent joint inversion we invert for baseline and monitor models while regularizing the difference between the models with this spatially varying confidence map. Unlike double difference full waveform inversion (DDFWI) we do not require identical source and receiver positions in the baseline and monitor surveys

Care of patients with pulmonary arterial hypertension during the coronavirus (COVID-19) pandemic

The COVID-19 pandemic presents many unique challenges when caring for patients with pulmonary hypertension. The COVID-19 pandemic has altered routine standard of care practice and the acute management particularly for those patients with pulmonary arterial hypertension, where pulmonary arterial hypertension-specific treatments are used. It is important to balance the ongoing care and evaluation of pulmonary arterial hypertension patients with exposure risk to COVID-19 for patients coming to clinic or the hospital. If there is a morbidity and mortality benefit from starting pulmonary arterial hypertension therapies, for example in a patient with high-likelihood of pulmonary arterial hypertension, then it remains important to complete the thorough evaluation. However, the COVID-19 outbreak may also represent a unique time when pulmonary hypertension experts have to weigh the risks and benefits of the diagnostic work-up including potential exposure to COVID-19 versus initiating targeted pulmonary arterial hypertension therapy in a select high-risk, high likelihood World Symposium Pulmonary Hypertension Group 1 pulmonary arterial hypertension patients. This document will highlight some of the issues facing providers, patients, and the pulmonary arterial hypertension community in real-time as the COVID-19 pandemic is evolving and is intended to share expected common clinical scenarios and best clinical practices to help the community at-large