Search for: All records

Mobile wireless networks present several challenges for any learning system, due to uncertain and variable device movement, a decentralized network architecture, and constraints on network resources. In this work, we use deep reinforcement learning (DRL) to learn a scalable and generalizable forwarding strategy for such networks. We make the following contributions: i) we use hierarchical RL to design DRL packet agents rather than device agents, to capture the packet forwarding decisions that are made over time and improve training efficiency; ii) we use relational features to ensure generalizability of the learned forwarding strategy to a wide range of network dynamics and enable offline training; and iii) we incorporate both forwarding goals and network resource considerations into packet decision-making by designing a weighted DRL reward function. Our results show that our DRL agent often achieves a similar delay per packet delivered as the optimal forwarding strategy and outperforms all other strategies including state-of-the-art strategies, even on scenarios on which the DRL agent was not trained. 

Kaposi's sarcoma–associated herpesvirus (KSHV) inhibitor of cyclic GMP–AMP synthase (cGAS) (KicGAS) encoded by ORF52 is a conserved major tegument protein of KSHV and the first reported viral inhibitor of cGAS. In our previous study, we found that KicGAS is highly oligomerized in solution and that oligomerization is required for its cooperative DNA binding and for inhibiting DNA-induced phase separation and activation of cGAS. However, how KicGAS oligomerizes remained unclear. Here, we present the crystal structure of KicGAS at 2.5 Å resolution, which reveals an “L”-shaped molecule with each arm of the L essentially formed by a single α helix (α1 and α2). Antiparallel dimerization of α2 helices from two KicGAS molecules leads to a unique “Z”-shaped dimer. Surprisingly, α1 is also a dimerization domain. It forms a parallel dimeric leucine zipper with the α1 from a neighboring dimer, leading to the formation of an infinite chain of KicGAS dimers. Residues involved in leucine zipper dimer formation are among the most conserved residues across ORF52 homologs of gammaherpesviruses. The self-oligomerization increases the valence and cooperativity of interaction with DNA. The resultant multivalent interaction is critical for the formation of liquid condensates with DNA and consequent sequestration of DNA from being sensed by cGAS, explaining its role in restricting cGAS activation. The structure presented here not only provides a mechanistic understanding of the function of KicGAS but also informs a molecular target for rational design of antivirals against KSHV and related viruses. 

Critical role of hydrogen bond network is unraveled by integrating nuclear quantum effects into nonadiabatic molecular dynamics. 

Crowd mobility prediction, in particular, forecasting flows at and transitions across different locations, is essential for crowd analytics and management in spacious environments featured with large gathering. We propose GAEFT, a novel crowd mobility analytics system based on the multi-task graph attention neural network to forecast crowd flows (inflows/outflows) and transitions. Specifically, we leverage the collective and sanitized campus Wi-Fi association data provided by our university information technology service and conduct a relatable case study. Our comprehensive data analysis reveals the important challenges of sparsity and skewness, as well as the complex spatio-temporal variations within the crowd mobility data. Therefore, we design a novel spatio-temporal clustering method to group Wi-Fi access points (APs) with similar transition features, and obtain more regular mobility features for model inputs. We then propose an attention-based graph embedding design to capture the correlations among the crowd flows and transitions, and jointly predict the AP-level flows as well as transitions across buildings and clusters through a multi-task formulation. Extensive experimental studies using more than 28 million association records collected during 2020-2021 academic year validate the excellent accuracy of GAEFT in forecasting dynamic and complex crowd mobility. 

Amorphous inorganic semiconductors have attracted growing interest due to their unique electrical and optical properties that arise from their intrinsic disordered structure and thermodynamic metastability. Recently, amorphous inorganic semiconductors have been applied in a variety of new technologies, including solar cells, photoelectrocatalysis, and photocatalysis. It has been reported that amorphous phases can improve both efficiency and stability in these applications. While these phenomena are well established, their mechanisms have long remained unclear. This review first introduces the general background of amorphous inorganic semiconductor properties and synthesis. Then, the recent successes and current challenges of amorphous inorganic semiconductor-based materials for applications in solar cells, photoelectrocatalysis, and photocatalysis are addressed. In particular, we discuss the mechanisms behind the remarkable performances of amorphous inorganic semiconductors in these fields. Finally, we provide insightful perspectives into further developments for applications of amorphous inorganic semiconductors. 

Aims. Flux ropes are generally believed to be core structures of solar eruptions that are significant for the space weather, but their formation mechanism remains intensely debated. We report on the formation of a tiny flux rope beneath clusters of active region loops on 2018 August 24. Methods. Combining the high-quality multiwavelength observations from multiple instruments, we studied the event in detail in the photosphere, chromosphere, and corona. Results. In the source region, the continual emergence of two positive polarities (P1 and P2) that appeared as two pores (A and B) is unambiguous. Interestingly, P2 and Pore B slowly approached P1 and Pore A, implying a magnetic flux convergence. During the emergence and convergence, P1 and P2 successively interacted with a minor negative polarity (N3) that emerged, which led to a continuous magnetic flux cancellation. As a result, the overlying loops became much sheared and finally evolved into a tiny twisted flux rope that was evidenced by a transient inverse S-shaped sigmoid, the twisted filament threads with blueshift and redshift signatures, and a hot channel. Conclusions. All the results show that the formation of the tiny flux rope in the center of the active region was closely associated with the continuous magnetic flux emergence, convergence, and cancellation in the photosphere. Hence, we suggest that the magnetic flux emergence, convergence, and cancellation are crucial for the formation of the tiny flux rope.