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1. Provable Policy Gradient Methods for Average-Reward Markov Potential Games

   Cheng, Min; Zhou, Ruida; Kumar, P R; Tian, Chao (May 2024, Proceedings of the 27th International Conference on Artificial Intelligence and Statistics (AISTATS) 2024)

   We study Markov potential games under the infinite horizon average reward criterion. Most previous studies have been for discounted rewards. We prove that both algorithms based on independent policy gradient and independent natural policy gradient converge globally to a Nash equilibrium for the average reward criterion. To set the stage for gradient-based methods, we first establish that the average reward is a smooth function of policies and provide sensitivity bounds for the differential value functions, under certain conditions on ergodicity and the second largest eigenvalue of the underlying Markov decision process (MDP). We prove that three algorithms, policy gradient, proximal-Q, and natural policy gradient (NPG), converge to an ϵ-Nash equilibrium with time complexity O(1ϵ2), given a gradient/differential Q function oracle. When policy gradients have to be estimated, we propose an algorithm with ~O(1mins,aπ(a|s)δ) sample complexity to achieve δ approximation error w.r.t~the ℓ2 norm. Equipped with the estimator, we derive the first sample complexity analysis for a policy gradient ascent algorithm, featuring a sample complexity of ~O(1/ϵ5). Simulation studies are presented. 

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2. How Hot Is Too Hot? Disentangling Mid‐Cretaceous Hothouse Paleoclimate From Diagenesis

   https://doi.org/10.1029/2022PA004517  

   Fetrow, A_C; Snell, K_E; Di_Fiori, R_V; Long, S_P; Bonde, J_W (November 2022, Paleoceanography and Paleoclimatology)

   Abstract The North American Newark Canyon Formation (NCF; ∼113–98 Ma) presents an opportunity to examine how terrestrial carbonate facies reflect different aspects of paleoclimate during one of the hottest periods of Earth's history. The lower NCF type section preserves heterogeneous palustrine facies and the upper NCF preserves lacustrine deposits. We combined carbonate facies analysis withδ¹³C,δ¹⁸O, and Δ₄₇data sets to assess which carbonate facies preserve stable isotope signals that are most representative of climatic conditions. Palustrine facies record the heterogeneity of the original wetland environment in which they formed. Using the pelmicrite facies that formed in deeper wetlands, we interpret a lower temperature zone (35–40°C) to reflect warm season water temperatures. In contrast, a mottled micrite facies which formed in shallower wetlands records hotter temperatures (36–68°C). These hotter temperatures reflect radiatively heated “bare‐skin” temperatures that occurred in a shallow depositional setting. The lower lacustrine unit has been secondarily altered by hydrothermal fluids while the upper lacustrine unit likely preserves primary temperatures andδ¹⁸O_waterof catchment‐integrated precipitation. Resultantly, the palustrine pelmicrite and lacustrine micrite are the facies most likely to reflect ambient climate conditions, and therefore, are the best facies to use for paleoclimate interpretations. Average warm season water temperatures of 41.1 ± 3.6°C and 37.8 ± 2.5°C are preserved by the palustrine pelmicrite (∼113–112 Ma) and lacustrine micrite (∼112–103 Ma), respectively. These data support previous interpretations of the mid‐Cretaceous as a hothouse climate and demonstrate the importance of characterizing facies for identifying the data most representative of past climates. 

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3. Syncontractional deposition of the Cretaceous Newark Canyon Formation, Diamond Mountains, Nevada: Implications for strain partitioning within the U.S. Cordillera

   https://doi.org/10.1130/GES02168.1  

   Di_Fiori, Russell V; Long, Sean P; Fetrow, Anne C; Snell, Kathryn E; Bonde, Joshua W; Vervoort, Jeff (January 2020, Geosphere)

   Abstract The timing of deformation and deposition within syntectonic basins provides critical information for understanding the evolution of strain in mountain belts. In the U.S. Cordillera, contractional deformation was partitioned between the Sevier thrust belt in Utah and several structural provinces in the hinterland in Nevada. One hinterland province, the Central Nevada thrust belt (CNTB), accommodated up to ∼15 km of shortening; however, in most places, this deformation can only be bracketed between Permian and Eocene. Cretaceous deposits of the Newark Canyon Formation (NCF), which are sparsely exposed along the length of the CNTB, offer the opportunity to constrain deformation timing. Here, we present mapping and U-Pb zircon geochronology from the NCF in the Diamond Mountains, which demonstrate deposition of the NCF during proximal CNTB deformation. Deposition of the basal NCF member was under way no earlier than ca. 114 Ma, a tuff in the middle part of the section was deposited at ca. 103 Ma, and the youngest member was deposited no earlier than ca. 99 Ma. Intraformational angular unconformities and abrupt along- and across-strike thickness changes indicate that NCF deposition was related to growth of an east-vergent fault-propagation fold. Clast compositions define unroofing of upper Paleozoic sedimentary rocks, which we interpret as the progressive erosion of an anticline ∼10 km to the west. CNTB deformation was contemporaneous with shortening in the Sevier thrust belt, which defines middle Cretaceous strain partitioning between frontal and interior components of the Cordillera. Strain partitioning may have been promoted by renewed underthrusting during a period of high-flux magmatism. 

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4. Tamper-sensitive pre-formed ReRAM-based PUFs: Methods and experimental validation

   https://doi.org/10.3389/fnano.2022.1055545  

   Wilson, Taylor; Cambou, Bertrand (November 2022, Frontiers in Nanotechnology)

   In this paper, we present the characterization of pre-formed resistive random access memories to design physical unclonable functions and experimentally validate inherent properties such as tamper sensitivity and a self-destroy mode. The physical unclonable functions were tested for repetitive use, temperature effects, and aging. The variations during successive response generation cycles and drift rates are quantized to explore their reliability. We define tamper-sensitivity as the ability to detect tampering attacks. To establish tamper sensitivity, the cells were characterized for higher current sweeps, and the injected current at which they break down is extracted and analyzed to determine suitable operating ranges. Our experimental results show that at least 91% of the cells can generate keys protected by the scheme, while 22% of the sensing elements are triggered. Finally, the cells were characterized for high Voltage sweeps to be able to destroy the physical unclonable functions on-demand when tampering activity is detected. A fixed Voltage of 1.9 V is enough to destroy the entire array. 

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5. Testing phase space properties of synchronous dynamical systems with nested canalyzing local functions.

   Rosenkrantz, D; Marathe, M; Ravi, S; Stearns, R (January 2018, AAMAS 2018)

   Discrete graphical dynamical systems serve as effective formal models in many contexts, including simulations of agent-based models, propagation of contagions in social networks and study of biological phenomena. A class of Boolean functions, called nested canalyzing functions (NCFs), has been used as a good model of certain biological phenomena. Motivated by these biological applications, we study a variety of analysis problems for synchronous graphical dynamical systems (SyDSs) over the Boolean domain, where each local function is an NCF. Each analysis problem involves testing whether the phase space of a given SyDS satisfies a certain property. We present intractability results for some properties as well as efficient algorithms for others. In several cases, our results clearly delineate intractable and efficiently solvable versions of problems 

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