Search for: All records

Abstract. We assessed the oxidative potential (OP) of both water-soluble andmethanol-soluble fractions of ambient fine particulate matter (PM2.5)in the Midwestern United States. A large set of PM2.5 samples (N=241) was collected from five sites set up in different environments, i.e.,urban, rural, and roadside, in Illinois, Indiana, and Missouri during May 2018–May 2019. Five acellular OP endpoints, including the consumption rate ofascorbic acid and glutathione in a surrogate lung fluid (SLF) (OPAA andOPGSH, respectively), dithiothreitol (DTT) depletion rate (OPDTT),and ⚫OH generation rate in SLF and DTT (OPOH−SLF andOPOH−DTT, respectively), were measured for all PM2.5 samples.PM2.5 mass concentrations in the Midwestern US as obtained from thesesamples were spatially homogeneously distributed, while most OP endpointsshowed significant spatiotemporal heterogeneity. Seasonally, higheractivities occurred in summer for most OP endpoints for both water- andmethanol-soluble extracts. Spatially, the roadside site showed the highestactivities for most OP endpoints in the water-soluble extracts, while onlyoccasional peaks were observed at urban sites in the methanol-soluble OP.Most OP endpoints showed similar spatiotemporal trends between mass- andvolume-normalized activities across different sites and seasons. Comparisonsbetween two solvents (i.e., water and methanol) showed that methanol-solubleOP generally had higher activity levels than corresponding water-soluble OP.Site-to-site comparisons of OP showed stronger correlations formethanol-soluble OP compared to water-soluble OP, indicating a betterextraction of water-insoluble redox-active compounds from various emissionsources into methanol. We found a weak correlation and inconsistent slopevalues between PM2.5 mass and most OP endpoints. Moreover, thepoor to moderate intercorrelations among different OP endpoints indicatedifferent mechanisms of OP represented by these endpoints and thusdemonstrate the rationale for analyzing multiple acellular endpoints for abetter and more comprehensive assessment of OP. 

Mobile Virtual Network Operators (MVNOs) are an increasingly growing segment of the market for wireless services. MVNOs do not own their own network infrastructure and so must cooperate with existing Mobile Network Operators (MNOs) to gain access to the network infrastructure needed to enter this market. Cooperating with an MVNO is a non-trivial decision for an MNO in part because the MVNO may then become a potential competitor for customers. One motive for entering into such an arrangement is that the MVNO receives an added value from serving customers beyond what it earns from charging them for wireless service. We study a game theoretic model for the cooperation and competition between an MNO and such an added value MVNO based on models for price competition with congestible resources. Our model captures two different dimensions of how an MNO may cooperate. The first dimension is the payment scheme between the MNO and the MVNO. The second dimension is the access priority that the MNO chooses to offer to the MVNO's customers. We characterize the pros and cons of different cooperation modes and analyze the optimal cooperation mode under different conditions. 

Conventionally, mobile network operators charge users for data plan subscriptions. To create new revenue streams, some operators now also incentivize users to watch ads with data rewards and collect payments from advertisers. In this work, we study two such rewarding schemes: a Subscription-Aware Rewarding (SAR) scheme and a Subscription-Unaware Rewarding (SUR) scheme. Under the SAR scheme, only the subscribers of the operators' existing data plans are eligible for the rewards; under the SUR scheme, all users are eligible for the rewards (e.g., the users who do not subscribe to the data plans can still get SIM cards and receive data rewards by watching ads). We model the interactions among a capacity-constrained operator, users, and advertisers by a two-stage Stackelberg game, and characterize their equilibrium strategies under both the SAR and SUR schemes. We show that the SAR scheme can lead to more subscriptions and a higher operator revenue from the data market, while the SUR scheme can lead to better ad viewership and a higher operator revenue from the ad market. We provide some counter-intuitive insights for the design of data rewards. For example, the operator's optimal choice between the two schemes is sensitive to the users' data consumption utility function. When each user has a logarithmic utility function, the operator should apply the SUR scheme (i.e., reward both subscribers and nonsubscribers) if and only if it has a small network capacity.