Direct methane conversion to methanol by ionic liquid-dissolved platinum catalysts

Ternary systems of inorganic Pt salts and oxides, ionic liquids and concentrated sulfuric acid are effective at catalyzing the direct, selective oxidation of methane to methanol and appear to be more water tolerant than the Catalytica reaction

Novel Broadband Amplifier for Mid-Infrared Semiconductor laser and applications in spectroscopy

An amplifier design for broadband Mid-IR buried-hetero (BH) structure epitaxial laser is presented, and external cavity design based on this amplifier is described. Spectroscopy results characterizing such single frequency lasers are demonstrated with whispering gallery mode CaF2 disc/ball, saturated absorption in hollow waveguide and direct chemical analysis in water

Massive MIMO Channel Modeling

Massive MIMO has attracted many researchers’ attention as it is a promising technology for future 5G communication systems. To characterize the propagation channels of the massive MIMO and to evaluate system performance, it is important to develop an accurate channel model for it. In this thesis, two correlative models, i.e., the Kronecker model and the Weichselberger model, and a cluster-based model, i.e., the Random Cluster Model (RCM), have been validated based on real-life data from four measurement campaigns. These measurements were performed at Lund University using two types of base station (BS) antenna arrays, a practical and compact uniform cylindrical array (UCA) and a physically-large virtual uniform linear array (ULA), both at 2.6 GHz. For correlative models, performance metrics such as channel capacity, sum-rate and singular value spread are examined to validate the model. The random cluster model, which is constructed and evaluated on a cluster level, has been parameterized and validated using the measured channel data. The correlative models are relatively simple and are suitable for analytical study. Validation results show that correlative models can reflect massive MIMO channel capacity and singular value spread, when the compact UCA is used at the base station and when users are closely located. However, for the physically-large ULA, correlative models tend to underestimate channel capacity. The RCM is relatively complex and is usually used for simulation purpose. Validation results show that the RCM is a promising model for massive MIMO channels, however, improvements are needed

Learning Adaptable Risk-Sensitive Policies to Coordinate in Multi-Agent General-Sum Games

In general-sum games, the interaction of self-interested learning agents commonly leads to socially worse outcomes, such as defect-defect in the iterated stag hunt (ISH). Previous works address this challenge by sharing rewards or shaping their opponents' learning process, which require too strong assumptions. In this paper, we demonstrate that agents trained to optimize expected returns are more likely to choose a safe action that leads to guaranteed but lower rewards. However, there typically exists a risky action that leads to higher rewards in the long run only if agents cooperate, e.g., cooperate-cooperate in ISH. To overcome this, we propose using action value distribution to characterize the decision's risk and corresponding potential payoffs. Specifically, we present Adaptable Risk-Sensitive Policy (ARSP). ARSP learns the distributions over agent's return and estimates a dynamic risk-seeking bonus to discover risky coordination strategies. Furthermore, to avoid overfitting training opponents, ARSP learns an auxiliary opponent modeling task to infer opponents' types and dynamically alter corresponding strategies during execution. Empirically, agents trained via ARSP can achieve stable coordination during training without accessing opponent's rewards or learning process, and can adapt to non-cooperative opponents during execution. To the best of our knowledge, it is the first method to learn coordination strategies between agents both in iterated prisoner's dilemma (IPD) and iterated stag hunt (ISH) without shaping opponents or rewards, and can adapt to opponents with distinct strategies during execution. Furthermore, we show that ARSP can be scaled to high-dimensional settings.Comment: arXiv admin note: substantial text overlap with arXiv:2205.1585

Design, Meshing Characteristics and Stress Analysis of Cylindrical Gears with Curvilinear Tooth Profile

Curvilinear tooth gears are commonly produced on a face milling cutter and a hob cutter. However, this paper proposes a kind of curvilinear tooth gear which is processed by a parallel linkage with a single blade cutter. For the purpose of identifying the meshing and contact characteristics of curvilinear tooth gears, the paper covers the following: (i) equations of tooth surfaces are deduced from the meshing theory, and a parameterized geometric model is developed by applying computer graphics; (ii) an investigation into meshing characteristics for an ideal assembly condition is performed, and an instantaneous contact curve is obtained from the developed tooth contact algorithm; (iii) based on the application of the finite element method, the evolution of contact and bending stresses during the cycle of meshing and between different arc radii of the curvilinear tooth is illustrated by numerical examples. The result shows that curvilinear tooth gear drives possess a higher contact ratio, severe contact stresses on the top edge of the tooth, and lower contact and bending stresses between appropriate arc radii, hence they may replace spur gears in the future