Browsing by Author "Yang, Yang"

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    Magnetism from bond-directional anisotropic interactions
    (2023-10) Yang, Yang
    This dissertation presents an overview of my research works on studying magnetism emerging from bond-directional interactions in spin-orbit coupled Mott insulators. The study encompasses two primary activities: the examination of superexchange spin models and the comprehension of magnetic excitations observed in real materials. The first activity includes the study of theoretical Kitaev-Heisenberg model on the kagome lattice, where we identify nontrivial local symmetry of the system. We find the classical and quantum phase diagrams of the model. Our findings reveal striking similarities of the physics between the classical and quantum regimes. The second activity mainly focuses on understanding of Raman responses (inelastic light scattering) from different materials. We first employ the Loudon-Fleury form of the Raman operator to elucidate magnetic excitations in the pyrochlore compound Nd2Ir2O7. Then we extend the Raman operator beyond the conventional Loudon- Fleury formalism, and apply it to understand magnetic excitations observed in the hyperhoneycomb material β-Li2IrO3.
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    Structural and Molecular Basis for Multifunctional Roles of Cellular Proteases
    (2015-09) Yang, Yang
    Cellular proteases were first known for their roles in processing peptides such as signal peptides. Recent discoveries have begun to unravel their multifunctional roles in many other biological processes including blood pressure regulation and virus infection. However, the knowledge gathered thus far is still limited regarding the underlying mechanisms for these functions. Therefore, my thesis research focuses on elucidating the structural and molecular basis for the multiple functions of several critical cellular proteases (aminopeptidase A (APA), dipeptidyl peptidase 4 (DPP4), proprotein convertases (PPC) and lysosomal cysteine proteases (LCP)). APA is well known for its role in blood pressure regulation, but the lack of its structure is a major obstacle for designing APA-targeting agents for the treatment of hypertension, which affects about one third of US adults. My study determined the crystal structures of APA in complex with a variety of substrates and inhibitors, and elaborated the substrate specificity of APA in physiological contexts. The structural information sheds light on the blood pressure regulation by APA, and lays the foundation for developing novel APA inhibitors to treat hypertension. DPP4 was recently identified as the receptor for the newly emerged Middle East respiratory syndrome coronavirus (MERS-CoV). To provide insights into the origin of MERS-CoV, I investigated the receptor usage and cell entry of MERS-CoV in comparison with HKU4, a related bat coronavirus. I discovered that DPP4 is also the receptor for HKU4. However, HKU4 failed to infect human cells because of its inability to use human cellular protease (e.g. PPC and LCP) for cell entry. PPC and LCP are critically involved in cell entry of many viruses. Here, I identified two residue differences between the spikes of MERS-CoV and HKU4 that account for their differential processes by human PPC and LCP, respectively. These results are critical for understanding the cross-species transmission of MERS-CoV, as well as for preventing the spread of related bat viruses. Taken together, the work presented in this thesis contributes to the overall understanding of the underlying mechanisms for diverse functions of cellular proteases in various health problems, and provides rationales for combating related health-threatening diseases.
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    Target-Driven Robotic Manipulation with Visual Attribute Reasoning
    (2022-07) Yang, Yang
    As robots move from factories to our daily lives, robotic manipulation for ordinaryusers is attracting more attention from the robotics community. Target-driven manipulation is a necessary function for robots to enter people’s everyday spaces because it enables robots to perform tasks (such as grasping a specific object) driven by user inputs. Three key challenges, however, preclude the development of target-driven robotic manipulation: (1) ambiguity caused by a mismatch between human referring and robot understanding; (2) clutter formed by a target object and its surrounding objects; (3) domain shift referring to the change of data distribution from training and deployment environments. In this thesis, we address these challenges by equipping target-driven robotic manipulation with visual attribute reasoning. People recognize and grasp a target object in daily scenes by remembering the critical properties of the target. Visual attribute reasoning, or the ability to perceive andreason about essential attributes of a target item, enables humans to understand the target object and its surroundings, as well as plan their actions accordingly. In this thesis, we present the categorization of visual attributes of objects and their crucial functions in robotic manipulation. We develop robotic manipulation systems that integrate object attributes in the form of appearances, spatial locations, and local relations. The robotic systems can accomplish target-driven tasks in challenging and unconstrained environments because of the integration of these object attributes. As a result, our research advances target-driven robotic manipulation in terms of clutter handling, model generalization, and human-robot interaction in particular. Our long-term goal is to develop intelligent robots that connect human users withtheir surrounding environments. Future robots are predicted to interact with humans and accomplish complex target-driven tasks that benefit users. This thesis makes a step towards the goal by leveraging visual attribute reasoning. We present robotic grasping systems that can locate an invisible target occluded in clutter, grasp a never-seen object based on appearance attributes, and disambiguate unclear commands guided by object attributes.