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Nongjian Tao – One of the best experts on this subject based on the ideXlab platform.

  • Charge-Based Detection of Small Molecules by Plasmonic-Based Electrochemical Impedance Microscopy
    Analytical chemistry, 2013
    Co-Authors: Christopher A. Macgriff, Shaopeng Wang, Peter Wiktor, Wei Wang, Xiaonan Shan, Nongjian Tao
    Abstract:

    Charge-based detection of small molecules is demonstrated by plasmonic-based electrochemical impedance microscopy (P-EIM). The dependence of surfAce plasmon resonance (SPR) on surfAce charge density is used to detect small molecules (60–120 Da) printed on a dextran-modified sensor surfAce. Local variations in charge density on an electrode surfAce are manifest in an optical SPR signal. The SPR response to an applied Ac potential measures the sensor surfAce impedance which is a function of the surfAce charge density. This optical signal is comprised of a dc and an Ac Component, and is measured with high spatspatial resolution. The dc element of the SPR signal represents conventional SPR imaging information. The amplitude and phase of local surfAce impedance is provided by the Ac Component. The phase signal of the small molecules is a function of their charge status, which is manipulated by the pH of a solution. Small molecules with positive, neutral, and negative charge are detected by P-EIM. This technique is…

  • Electron transport in single molecules measured by a distance-modulation assisted break junction method.
    Nano letters, 2008
    Co-Authors: Jilin Xia, Ismael Díez-pérez, Nongjian Tao
    Abstract:

    We describe a method to determine whether a measured current in a break junction is due to electron tunneling via spAce or conduction through a molecule bridged between two electrodes. By modulating the electrode separation, we monitor both the DC and the Ac Components of the current. The Ac Component indicates if a molecule is connected to the electrodes while the DC Component is the transport current through the molecule. This method allows us to remove the tunneling bAckground from conductance histograms and unambiguously measure the I−V charActeristic of single molecules. Furthermore, it provides valuable information about the electromechanical properties of single molecules.

  • SurfAce impedance imaging technique.
    Analytical chemistry, 2008
    Co-Authors: Kyle J. Foley, Xiaonan Shan, Nongjian Tao
    Abstract:

    We demonstrate here a surfAce impedance imaging technique based on sensitive dependence of surfAce plasmon resonance (SPR) on local surfAce charge density. By applying a potential modulation to a sensor surfAce, we are able to simultaneously obtain three images: the dc Component and the amplitude and phase of the Ac Component. The dc image measures local molecular binding Activity on the surfAce, as found in the conventional SPR imaging technique, and the Ac images are directly related to the local impedance of the surfAce. Our experimental data can be analyzed quantitatively in terms of the simple free elecelectron gas<gas model for the sensor surfAce and the Randles equivalent circcircuit model for interfAcial impedance.

Zhengyu Lu – One of the best experts on this subject based on the ideXlab platform.

  • online updating of rotor time constant based on combined voltage and current mode flux observer for speed sensorless Ac drives
    IEEE Transactions on Industrial Electronics, 2014
    Co-Authors: Kai Wang, Bin Chen, Guangtong Shen, Wenxi Yao, Kevin Lee, Zhengyu Lu
    Abstract:

    The simultaneous online estimation algorithm of rotor time constant and rotor speed for a speed-sensorless induction mAchine is proposed. With a small signal injected to the flux command, the method can Accurately complete the online tuning of Tr over a wide range of speed estimation, including the rated speed and the very low speed of 1 Hz or even lower speeds under both no-load and loaded operations. Sensitivity of stator resistance error is studied, and the impAct of stator resistance error on this method is severely reduced by the closed-loop structure of combined voltage and current (UI) mode flux observer. The identification process only needs the Ac Component amplitude without considering Ac Component phase drifts; thus, the division by zero at the zero-crossing point is avoided, which greatly increases the AccurAcy. Furthermore, any differential integral operations or even a filter is not needed; hence, the computation is rather simple and time saving. Moreover, unlike other signal injection methods, there are no special requirements on the injected signal frequency. The AccurAcy and validity of the method has been verified by Matrix Laboratory simulation model. Further experimental results on a 2.2-kW 50-Hz 4-pole induction motor also show effectiveness of this proposed method.

Zdenek Peroutka – One of the best experts on this subject based on the ideXlab platform.

I. N. Askerzade – One of the best experts on this subject based on the ideXlab platform.

Kai Wang – One of the best experts on this subject based on the ideXlab platform.

  • online updating of rotor time constant based on combined voltage and current mode flux observer for speed sensorless Ac drives
    IEEE Transactions on Industrial Electronics, 2014
    Co-Authors: Kai Wang, Bin Chen, Guangtong Shen, Wenxi Yao, Kevin Lee, Zhengyu Lu
    Abstract:

    The simultaneous online estimation algorithm of rotor time constant and rotor speed for a speed-sensorless induction mAchine is proposed. With a small signal injected to the flux command, the method can Accurately complete the online tuning of Tr over a wide range of speed estimation, including the rated speed and the very low speed of 1 Hz or even lower speeds under both no-load and loaded operations. Sensitivity of stator resistance error is studied, and the impAct of stator resistance error on this method is severely reduced by the closed-loop structure of combined voltage and current (UI) mode flux observer. The identification process only needs the Ac Component amplitude without considering Ac Component phase drifts; thus, the division by zero at the zero-crossing point is avoided, which greatly increases the AccurAcy. Furthermore, any differential integral operations or even a filter is not needed; hence, the computation is rather simple and time saving. Moreover, unlike other signal injection methods, there are no special requirements on the injected signal frequency. The AccurAcy and validity of the method has been verified by Matrix Laboratory simulation model. Further experimental results on a 2.2-kW 50-Hz 4-pole induction motor also show effectiveness of this proposed method.