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Free, publiclyaccessible full text available December 1, 2024

Free, publiclyaccessible full text available July 1, 2024

Rockphysics models for carbonate reservoirs assume that the mineral elastic moduli are known variables. A review of publications reveals a range of values for calcite that are out of date and misleading. We present a robust compilation for future investigations. We subsequently discuss the application of calcite elastic moduli for rockphysics modeling and interpretation of wireline data through a case study data set from an offshore Canada carbonate reservoir. The data set exhibits an offset between the zeroporosity intercept and the calcite elastic moduli values. Our experience indicates that this phenomenon is present in many wireline data sets from carbonate reservoirs around the world. We demonstrate that the data can be reconciled to the mineral elastic moduli through the interpretation of microcracks in the formation (defined by a crack density of 0.06). Understanding the microcrack effect in relatively lowporosity formations is important for the correct calibration of pore microstructure parameters and for fluidsubstitution calculations. Results in the case study data set show a relatively high sensitivity to changes in fluid saturation. The sensitivity can be reduced through the use of effective mineral elastic moduli that are derived from the data. We justify the effective mineral elastic moduli as a representation of the mineral moduli plus microcracks. The effective mineral elastic moduli are proposed as a relatively simple method to constrain the fluid substitution calculations in lowporosity formations where microcracks are present.more » « lessFree, publiclyaccessible full text available April 1, 2024

This paper investigates when one can efficiently recover an approximate Nash Equilibrium (NE) in offline congestion games. The existing dataset coverage assumption in offline generalsum games inevitably incurs a dependency on the number of actions, which can be exponentially large in congestion games. We consider three different types of feedback with decreasing revealed information. Starting from the facilitylevel (a.k.a., semibandit) feedback, we propose a novel oneunit deviation coverage condition and show a pessimismtype algorithm that can recover an approximate NE. For the agentlevel (a.k.a., bandit) feedback setting, interestingly, we show the oneunit deviation coverage condition is not sufficient. On the other hand, we convert the game to multiagent linear bandits and show that with a generalized data coverage assumption in offline linear bandits, we can efficiently recover the approximate NE. Lastly, we consider a novel type of feedback, the gamelevel feedback where only the total reward from all agents is revealed. Again, we show the coverage assumption for the agentlevel feedback setting is insufficient in the gamelevel feedback setting, and with a stronger version of the data coverage assumption for linear bandits, we can recover an approximate NE. Together, our results constitute the first study of offline congestion games and imply formal separations between different types of feedback.more » « lessFree, publiclyaccessible full text available February 1, 2024

Free, publiclyaccessible full text available January 1, 2024

Free, publiclyaccessible full text available January 1, 2024

In this paper, we investigate Nashregret minimization in congestion games, a class of games with benign theoretical structure and broad realworld applications. We first propose a centralized algorithm based on the optimism in the face of uncertainty principle for congestion games with (semi)bandit feedback, and obtain finitesample guarantees. Then we propose a decentralized algorithm via a novel combination of the FrankWolfe method and Goptimal design. By exploiting the structure of the congestion game, we show the sample complexity of both algorithms depends only polynomially on the number of players and the number of facilities, but not the size of the action set, which can be exponentially large in terms of the number of facilities. We further define a new problem class, Markov congestion games, which allows us to model the nonstationarity in congestion games. We propose a centralized algorithm for Markov congestion games, whose sample complexity again has only polynomial dependence on all relevant problem parameters, but not the size of the action set.more » « less

We study algorithms using randomized value functions for exploration in reinforcement learning. This type of algorithms enjoys appealing empirical performance. We show that when we use 1) a single random seed in each episode, and 2) a Bernsteintype magnitude of noise, we obtain a worstcase O~(H√SAT) regret bound for episodic timeinhomogeneous Markov Decision Process where S is the size of state space, A is the size of action space, H is the planning horizon and T is the number of interactions. This bound polynomially improves all existing bounds for algorithms based on randomized value functions, and for the first time, matches the Ω(H√SAT) lower bound up to logarithmic factors. Our result highlights that randomized exploration can be nearoptimal, which was previously achieved only by optimistic algorithms. To achieve the desired result, we develop 1) a new clipping operation to ensure both the probability of being optimistic and the probability of being pessimistic are lower bounded by a constant, and 2) a new recursive formula for the absolute value of estimation errors to analyze the regret.more » « less

Sulfoximines are emerging moieties for medicinal and biological chemistry, due in part to their efficacy in selective inhibition of amideforming enzymes such as γglutamylcysteine synthetase. While smallmolecule sulfoximines such as methionine sulfoximine (MSO) and its derivatives are well studied, structures with methionine sulfoximine residues within complex polypeptides have been generally inaccessible. This paper describes a straightforward means of latestage onestep oxidation of methionine residues within polypeptides to afford NHsulfoximines. We also present chemoselective subsequent elaboration, most notably by copper( ii )mediated N–H crosscoupling at methionine sulfoximine residues with arylboronic acid reagents. This development serves as a strategy to incorporate diverse sulfoximine structures within natural polypeptides, and also identifies the methionine sulfoximine residue as a new site for bioorthogonal, chemoselective bioconjugation.more » « less

Abstract Explosive cyclones (ECs), defined as extratropical cyclones that experience normalized pressure drops of at least 24 hPa in 24 h, are impactful weather events in the North Atlantic sector, but yeartoyear changes in the frequency and impacts of these storms are sizeable. To analyze the sources of this interannual variability, we track cases of ECs and dissect them into two spatial groups: those that formed near the east coast of North America (coastal) and those in the north central Atlantic (high latitude). The frequency of highlatitude ECs is strongly correlated with the North Atlantic Oscillation, a wellknown feature, whereas coastal EC frequency is statistically linked with an atmospheric wave train emanating from the North Pacific in the last 30 years. This wave train pattern of alternating high and low pressure is associated with heightened upperlevel divergence and Eady growth rates along the east coast of North America, likely resulting in a stronger correspondence between the atmospheric wave train and coastal EC frequency. Using coupled model experiments, we show that the tropical and North Pacific oceans are an important factor for this atmospheric wave train and the subsequent enhancement of seasonal baroclinicity in the North Atlantic.