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The novel coronavirus responsible for COVID-19 was first identified in Hubei Province, China in December, 2019. Within a matter of months the virus had spread and become a global pandemic. In addition to international air travel, local travel (e.g. by passenger car) contributes to the geographic spread of COVID-19. We modify the common susceptible-exposed-infectious-removed (SEIR) virus spread model and investigate the extent to which short-term travel associated with driving influences the spread of the virus. We consider the case study of the US state of Minnesota, and calibrated the proposed model with travel and viral spread data. Using our modified SEIR model that considers local short-term travel, we are able to better explain the virus spread than using the long-term travel SEIR model. Short-term travel associated with driving is predicted to be a significant contributor to the historical and future spread of COVID-19. The calibrated model also predicts the proportion of infections that were detected. We find that if driving trips remain at current levels, a substantial increase in COVID-19 cases may be observed in Minnesota, while decreasing intrastate travel could help contain the virus spread., Competing Interests: The authors have declared that no competing interests exist.

In this letter we present a deterministic discrete-time networked SEIR model that includes a number of transportation networks, and present assumptions under which it is well defined. We analyze the limiting behavior of the model and present necessary and sufficient conditions for estimating the spreading parameters from data. We illustrate these results via simulation and with real COVID-19 data from the Northeast United States, integrating transportation data into the results.

Cobalt oxides, including spinel Co 3 O 4 and rock-salt CoO, have been widely reported as promising catalysts for oxygen reduction reaction (ORR). However, three types of cobalt ions, i.e., Co 2+ in the tetrahedral site (Co 2+ T d ), Co 3+ in the octahedral site (Co 3+ O h ), and Co 2+ in the octahedral site (Co 2+ O h ), are included in these oxides, and the roles of cobalt geometric occupancy and valance states have remained elusive. Here, for the first time, we investigated the effects of cobalt geometric occupancy on the ORR activity by substituting Co 2+ T d and Co 3+ O h of Co 3 O 4 with inactive Zn 2+ and Al 3+ , respectively. The ORR activity decreases in the order of Co 3 O 4 (Co 3+ O h , Co 2+ T d ) < ZnCo 2 O 4 (Co 3+ O h ) ≪ CoAl 2 O 4 (Co 2+ T d ) in accordance with the ORR overpotentials at the current density of 0.1 mA cm Ox -2 . Furthermore, by comparatively investigating the activity and stability of Co 3 O 4 (Co 3+ O h ) and CoO (Co 2+ O h ) nanoparticles, by virtue of the electrochemical technique, the high-resolution transmission electron microscopy, and the in operando fuel cell-X-ray absorption spectroscopy techniques, it was revealed that Co 2+ O h in CoO is the main active site, which under electrochemical conditions tends to transform into Co 3+ O h and form Co 3 O 4 with a hollow structure due to the Kirkendall effect; nevertheless, it retains decent ORR activity due to the formation of the unique hollow structure.