Browsing by Author "Zhang, Qing"
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Item Estimating a cost-effective individualized treatment rule (CE-ITR) based on machine learning(University of Delaware, 2021) Zhang, QingPolicy makers employ Cost-Effectiveness Analysis (CEA) to evaluate a new treatment based on its cost and effectiveness. ITR is the treatment recommendation based on patient’s characteristics. However, the recommends generated from ITR and CEA could mismatch, even opposite since their aim is different. Therefore, policy makers need a tool to trade-off between ITR and CEA. Traditionally, optimal ITR focus on the mean benefit on population level, not on individual level. In the era of precision medicine, an ideal intervention needs to be optimized based on individual level. ☐ Here a composite outcome, Net Monetary Benefit (NMB) which integrates the clinical benefits and corresponding cost, is adopted to address the optimization of the cost-effective ITR. ITR is taken as a function of patients’ characteristics that, when implemented, optimizes the allocation of limited healthcare resources by optimizing clinical benefits while minimizing treatment-related costs. Applying machine learning approach –conditional random forest and others(such as XGBoost) we can consider ITR and CEA jointly on individual level to estimate a Cost-Effective ITR(CE-ITR) and apply it to real world clinical data.Item Non-Monotonic Capacitance Change of Layered Ti3C2Tx MXene Film Structures under Increasing Compressive Stress(Advanced Functional Materials, 2022-12-09) Zhang, Qing; Ning, Ran; Cao, Jinxin; Song, Qingrui; Ye, Jiaxin; Wei, BingqingThe progress in advanced electronic devices has imposed a great demand for developing flexible electrochemical power devices, which requires a comprehensive understanding of the mechanical–electrochemical coupling behavior of various energy storage materials. Unlike a monotonic capacitance increase of carbon-based double-layer supercapacitors, MXene-based flexible supercapacitors demonstrate a non-monotonic, i.e., “increase-then-decrease” capacitance behavior under the pressure range of 8488 kPa. This non-monotonic capacitance response to pressure is intrinsic to the MXene film as its charge storage is primarily determined by the surface activity, which can be readily affected by pressure-induced dissociation of functionalities, as well as the charge transporting kinetics as limited by the inherent layered structure. The findings described in this study not only expand the knowledge of mechanical–electrochemical coupling to layered MXenes under pressure, but also give a vital design guideline for flexible/stretchable MXene-based energy storage devices or other electronics.Item Self-discharge of carbon materials-based electrochemical capacitors(University of Delaware, 2014) Zhang, QingSuffering from poor energy retention, electrochemical capacitors (ECs), with exceptional power capability and long-term cyclability compared to batteries, have rarely been considered as an energy storage device that can store energy enduringly. To develop ECs as a competitive alternative to batteries, it is critical and necessary to realize control over ECs' self-discharge for desired energy retention. This dissertation covers the pioneering progress made in establishing self-discharge mechanisms, realizing tunable self-discharge and making further insights into capacitive behaviors of ECs beyond self-discharge. Self-discharge mechanisms have been explored on ECs built with three typical carbon materials: single-walled carbon nanotubes (SWNT), graphene oxide (GO), and activated carbon fibers (ACF). Our research indicates that ECs' structures determine the relative strength between the two self-discharge driving forces: the potential field Δ E and the concentration gradient ∂c/∂x, and eventually affect the self-discharge mechanisms. For the ACF-LiPF6 EC with a high specific capacitance (i.e., high ∂c/∂x ) and relatively poor charge transportation (i.e., low ΔE ), its self-discharge is driven by ∂c/∂x and obeys the diffusion control model; for the SWNT-TEABF4 EC with good charge transportation and a relatively low specific capacitance, its self-discharge is driven by Δ E and obeys the potential driving model; and for the ACF-TEABF 4 EC with the two comparable driving forces, the dual mechanism model has been proposed. The self-discharge mechanism is extendable to GO based solid-state ECs. Nevertheless, factors such as temperature have no effects on self-discharge mechanisms though can affect the discharge rate of the self-discharge process. Moreover, through tailoring the functional groups on the SWNT surface, tuning of the self-discharge has been realized for the first time on the SWNT-TEABF 4 EC. This breakthrough will offer a facile and feasible solution to the appeal for capacitor components with specialized energy retention in electric circuit designs. Interesting contradiction between considerable energy density and undetectable ionic diffusion has been observed on the GO based solid-state ECs, which challenges the conventional understanding of ECs and dielectric capacitors (DCs). From systematical characterizations and modeling calculations, the Charge Close-Packed model has been proposed, featuring periodical layers of charges as well as nanoscaled ionic diffusion and well explaining the contradiction observed on this GO based EC.