Single-Atom Switches and Single-Atom Gaps Using Stretched Metal Nanowires

Wang, Qingling,Liu, Ran,Xiang, Dong,Sun, Mingyu,Zhao, Zhikai,Sun, Lu,Mei, Tingting,Wu, Pengfei,Liu, Haitao,Guo, Xuefeng,Li, Zong-Liang,Lee, Takhee American Chemical Society 2016 ACS NANO Vol.10 No.10

<P>Utilizing individual atoms or molecules as functional units in electronic circuits meets the increasing technical demands for the miniaturization of traditional semiconductor devices. To be of technological interest, these functional devices should be high-yield, consume low amounts of energy, and operate at room temperature. In this study, we developed nanodevices called quantized conductance atomic switches (QCAS) that satisfy these requirements. The QCAS operates by applying a feedback-controlled voltage to a nanoconstriction within a stretched nanowire. We demonstrated that individual metal atoms could be removed from the nanoconstriction and that the removed metal atoms could be refilled into the nanoconstriction, thus yielding a reversible quantized conductance switch. We determined the key parameters for the QCAS between the 'on' and 'off' states at room temperature under a small operating voltage. By controlling the applied bias voltage, the atoms can be further completely removed from the constriction to break the nanowire, generating single-atom nanogaps. These atomic nanogaps are quite stable under a sweeping voltage and can be readjusted with subangstrom accuracy, thus fulfilling the requirement of both reliability and flexibility for the high-yield fabrication of molecular devices.</P>

Analysis on Slope Stability Considering Seepage Effect on Effective Stress

Yuanzhan Wang,Xufei Liu,Zhikai Zhang,Panbo Yang 대한토목학회 2016 KSCE JOURNAL OF CIVIL ENGINEERING Vol.20 No.6

Interaction between seepage field and soil stress field influences soil effective stress in general consideration. In addition, water erosion in soil skeleton can also affect soil effective stress. The current studies conducted triaxial compression experiments with seepage, Duncan-Chang model analysis, ABAQUS numerical simulation and followed by a case study analysis. Experiments show that the water erosion in soil skeleton reduces effective stress strength of soil, which is quantitatively described by the reduction of equivalent confining pressure. Through analyzing the characteristics of soil stress-strain curves, the equivalent confining pressure is applied to improve Duncan-Chang model. Using the modified Duncan-Chang model as well as considering the interaction between seepage field and soil stress field, ABAQUS software package is employed to simulate triaxial compression experiments with seepage. This method is validated by comparing simulation and experimental results. Furthermore, this method is applied in the case study of the overall stability of bank slope under seepage effect and finds that the modified model is more conservative on safety assessment of slope stability. The studies provided evidences to prove the importance of considering soil skeleton eroded by water flow in slope stability analysis quantitatively and proposed a modified Duncan-Chang model for engineering application with consideration of seepage effect.

On-Chip Break Junctions and Period-Adjustable Grating Driven by Thermal Stress

Ling Wang,Zhikai Zhao,Dong Xiang 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2017 NANO Vol.12 No.11

"The investigation of the electron transport through single molecule needs an efficient method to generate stable molecular junctions. There are various techniques, such as mechanically controllable break junction (MCBJ) technique and electromigration technique, to generate stable nanogaps and stable molecular junctions. However, it is a great challenge for MCBJ technique to obtain on-chip molecular junctions because of the constraint of the push rod components, which do not make it facile to fabricate highly integrated molecular devices. Meanwhile, the gap size between electrodes is nonadjustable for the electromigration method, which leads to a low yield of molecular junctions. In this report, a thermally controllable break junction method, which can overcome the above problem, is proposed for the first time. The device is based on a double-V-shaped symmetrical structure and mechanically driven by thermal expansion, thus the push rod is not needed. Furthermore, we proposed that the thermally controlled double-V-shaped structure can be employed to precisely adjust the period of the metal grating with nanometer accuracy, which is unavailable in other methods. "

Generic Adaptive Sliding Mode Control for a Quadrotor UAV System Subject to Severe Parametric Uncertainties and Fully Unknown External Disturbance

Tianpeng Huang,Deqing Huang,Zhikai Wang,Xi Dai,Awais Shah 제어·로봇·시스템학회 2021 International Journal of Control, Automation, and Vol.19 No.2

This paper aims to provide a generic robust controller that is able to manipulate all kinds of quadrotor unmanned aerial vehicle (UAV) systems automatically or adaptively in the presence of severe parametric uncertainties and fully unknown external disturbance. The dynamic model of the quadrotor is first obtained using Newton-Euler equations. Then, considering the underactuated and the strongly coupled characteristics of the quadrotor system, a nonlinear adaptive sliding mode control (ASMC) scheme is proposed. Meanwhile, additional adaptive laws are designed to estimate all the parameters of the quadrotor system, which in principle are difficult to be measured directly and accurately. Furthermore, to guarantee the asymptotic stability of the closed-loop system, the upper bound of the fully unknown external disturbance is estimated and adopted as the switching gain of the ASMC. Finally, simulations and experiments are carried out to illustrate the effectiveness and robustness of the proposed control scheme, where the superiority to linear quadratic control (LQR) and active disturbance rejection control (ADRC) has been demonstrated clearly.

Collateral Flow in Magnetic Resonance Angiography: Prognostic Value for Vertebrobasilar Stenosis With Stroke Recurrence

Long Yan,Ying Yu,Kaijiang Kang,Zhikai Hou,Min Wan,Weilun Fu,Rongrong Cui,Yongjun Wang,Zhongrong Miao,Xin Lou,Ning Ma 대한신경과학회 2022 Journal of Clinical Neurology Vol.18 No.5

Background and Purpose Intracranial vertebrobasilar atherosclerotic stenosis (IVBAS) is a major cause of posterior circulation stroke. Some patients suffer from stroke recurrence despite receiving medical treatment. This study aimed to determine the prognostic value of a new score for the posterior communicating artery and the P1 segment of the posterior cerebral artery (PCoA-P1) for predicting stroke recurrence in IVBAS. Methods We retrospectively enrolled patients with severe IVBAS (70%–99%). According to the number of stroke recurrences, patients were divided into no-recurrence, single-recurrence, and multiple-recurrences groups. We developed a new 5-point grading scale, with the PCoA-P1 score ranging from 0 to 4 based on magnetic resonance angiography, in which primary collaterals were dichotomized into good (2–4 points) and poor (0 or 1 point). Stroke recurrences after the index stroke were recorded. Patients who did not experience stroke recurrence were compared with those who experienced single or multiple stroke recurrences. Results From January 2012 to December 2019, 176 patients were enrolled, of which 116 (65.9%) had no stroke recurrence, 35 (19.9%) had a single stroke recurrence, and 25 (14.2%) had multiple stroke recurrences. Patients with single stroke recurrence (odds ratio [OR]= 4.134, 95% confidence interval [CI]=1.822–9.380, p=0.001) and multiple stroke recurrences (OR=6.894, 95% CI=2.489–19.092, p<0.001) were more likely to have poor primary collaterals than those with no stroke recurrence. Conclusions The new PCoA-P1 score appears to provide improve predictions of stroke recurrence in patients with IVBAS

Molecular Orbital Gating Surface-Enhanced Raman Scattering

Guo, Chenyang,Chen, Xing,Ding, Song-Yuan,Mayer, Dirk,Wang, Qingling,Zhao, Zhikai,Ni, Lifa,Liu, Haitao,Lee, Takhee,Xu, Bingqian,Xiang, Dong American Chemical Society 2018 ACS NANO Vol.12 No.11

<P>One of the promising approaches to meet the urgent demand for further device miniaturization is to create functional devices using single molecules. Although various single-molecule electronic devices have been demonstrated recently, single-molecule optical devices which use external stimulations to control the optical response of a single molecule have rarely been reported. Here, we propose and demonstrate a field-effect Raman scattering (FERS) device with a single molecule, an optical counterpart to field-effect transistors (a key component of modern electronics). With our devices, the gap size between electrodes can be precisely adjusted at subangstrom accuracy to form single molecular junctions as well as to reach the maximum performance of Raman scattering via plasmonic enhancement. Based on this maximum performance, we demonstrated that the intensity of Raman scattering can be further enhanced by an additional ∼40% if the orbitals of the molecules bridged two electrodes were shifted by a gating voltage. This finding not only provides a method to increase the sensitivity of Raman scattering beyond the limit of plasmonic enhancement, but also makes it feasible to realize addressable functional FERS devices with a gate electrode array.</P> [FIG OMISSION]</BR>

Rapid Identification and Characterization of Antioxidants from Ligularia fischeri

Xiang-Lan Piao,Xiao-Yuan Mi,Yan-Ze Tian,Qian Wu,Hui-Shan Piao,Zhikai Zeng,Xiangshu Piao,Ding Wang 대한약학회 2009 Archives of Pharmacal Research Vol.32 No.12

The objectives of this study were to investigate the radical-scavenging activity of Ligularia fischeri on oxidative damage by the radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) and to rapidly identify the active components using the bioassay-linked fractionation method. The MeOH extract and fractions of CH2Cl2, BuOH, and H2O from L. fischeri showed DPPH radical-scavenging effects in a dose-dependent manner (p < 0.01). In particular, the BuOH fraction had the most effective (p < 0.05) antioxidative capacity. The active constituents from the BuOH fraction of L. fischeri were rapidly isolated by bioassay-linked HPLC method and identified as hyperoside and 2''-acetylhyperoside with potent antioxidant effects against the DPPH radical, with IC50 values of 1.31 and 7.09 μg/mL, respectively. They have not been reported from L. fischeri yet.