Browsing by Author "Zhu, Jie"

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    Dynamic structural evolution of iron catalysts involving competitive oxidation and carburization during CO2 hydrogenation
    (AAAS, 2022) Zhu, Jie; Wang, Peng; Zhang, Xiaoben; Zhang, Guanghui; Li, Rongtan; Li, Wenhui; Senftle, Thomas P.; Liu, Wei; Wang, Jianyang; Wang, Yanli; Zhang, Anfeng; Fu, Qiang; Song, Chunshan; Guo, Xinwen
    Identifying the dynamic structure of heterogeneous catalysts is crucial for the rational design of new ones. In this contribution, the structural evolution of Fe(0) catalysts during CO2 hydrogenation to hydrocarbons has been investigated by using several (quasi) in situ techniques. Upon initial reduction, Fe species are carburized to Fe3C and then to Fe5C2. The by-product of CO2 hydrogenation, H2O, oxidizes the iron carbide to Fe3O4. The formation of Fe3O4@(Fe5C2+Fe3O4) core-shell structure was observed at steady state, and the surface composition depends on the balance of oxidation and carburization, where water plays a key role in the oxidation. The performance of CO2 hydrogenation was also correlated with the dynamic surface structure. Theoretical calculations and controll experiments reveal the interdependence between the phase transition and reactive environment. We also suggest a practical way to tune the competitive reactions to maintain an Fe5C2-rich surface for a desired C2+ productivity.
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    Membrane potential drives the exit from pluripotency and cell fate commitment via calcium and mTOR
    (Springer Nature, 2022) Sempou, Emily; Kostiuk, Valentyna; Zhu, Jie; Cecilia Guerra, M.; Tyan, Leonid; Hwang, Woong; Camacho-Aguilar, Elena; Caplan, Michael J.; Zenisek, David; Warmflash, Aryeh; Owens, Nick D. L.; Khokha, Mustafa K.
    Transitioning from pluripotency to differentiated cell fates is fundamental to both embryonic development and adult tissue homeostasis. Improving our understanding of this transition would facilitate our ability to manipulate pluripotent cells into tissues for therapeutic use. Here, we show that membrane voltage (Vm) regulates the exit from pluripotency and the onset of germ layer differentiation in the embryo, a process that affects both gastrulation and left-right patterning. By examining candidate genes of congenital heart disease and heterotaxy, we identify KCNH6, a member of the ether-a-go-go class of potassium channels that hyperpolarizes the Vm and thus limits the activation of voltage gated calcium channels, lowering intracellular calcium. In pluripotent embryonic cells, depletion of kcnh6 leads to membrane depolarization, elevation of intracellular calcium levels, and the maintenance of a pluripotent state at the expense of differentiation into ectodermal and myogenic lineages. Using high-resolution temporal transcriptome analysis, we identify the gene regulatory networks downstream of membrane depolarization and calcium signaling and discover that inhibition of the mTOR pathway transitions the pluripotent cell to a differentiated fate. By manipulating Vm using a suite of tools, we establish a bioelectric pathway that regulates pluripotency in vertebrates, including human embryonic stem cells.
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    Processing and characterization of lithium niobate thin films for ferroelectric nonvolatile memory applications
    (2002) Zhu, Jie; Rabson, Thomas A.
    Both highly c-axis and randomly-oriented LiNbO3 thin films are grown on p-type Si (111) substrates by RF magnetron sputtering and metallo-organic decomposition (MOD), respectively. Ellipsometry, X-ray diffraction, AFM and SEM are used to analyze the structural quality of the deposited ferroelectric thin films, including thickness, crystallinity, stoichiometry and surface roughness. Metal-ferroelectric-semiconductor structures are fabricated and electrically characterized with polarization vs. electric field (P-E) and capacitance vs. voltage (C-V) measurements. Hysteresis curves based on polarization switching are observed, verifying the ferroelectricity of deposited LiNbO3 thin films. Comparison of different film growth mechanisms between these two deposition methods is made, and their effects on physical and electrical characteristics of the derived LiNbO3 thin films are discussed. RF magnetron sputtering is proved to be a more promising thin-film growth technique than MOD for ferroelectric nonvolatile memory applications.