Origin of threshold current density for asymmetric magnetoresistance in Pt/Py bilayers

Li, Tian,Kim, Sanghoon,Lee, Seung-Jae,Lee, Seo-Won,Koyama, Tomohiro,Chiba, Daichi,Moriyama, Takahiro,Lee, Kyung-Jin,Kim, Kab-Jin,Ono, Teruo JAPAN SOCIETY OF APPLIED PHYSICS 2017 Applied physics express Vol.10 No.7

<P>The asymmetric magnetoresistance (MR) in Py/Pt bilayers is investigated. It increases linearly with respect to the current density up to a threshold and increases more rapidly above this threshold. To reveal the origin of the threshold behavior, we investigate the magnetic field dependence of the asymmetric MR. It is found that the magnetic field strongly suppresses the asymmetric MR only above the threshold current density. Micromagnetic simulation reveals that the reduction of magnetization due to the spin-torque oscillation can be the origin of the threshold behavior of the asymmetric MR. (C) 2017 The Japan Society of Applied Physics</P>

Comparing the efficacy of two different temperature stimulation in warm acupuncture on acute low back pain: A randomized controlled trial

Li Tian,Wang Siyao,Cheng Ke,Sun Lu,Jin Daopeng,Zhang Shen,Yang Zhen,Huang Zouqin 한국한의학연구원 2022 Integrative Medicine Research Vol.11 No.1

Background: Warm acupuncture, a combination of the mechanical stimulation of acupuncture and thermal stimulation of moxibustion, is commonly used in treating acute low back pain (LBP). This trial aimed to compare the efficacy of stronger (above 43°C) and weaker (above 40°C) heat stimulation in warm acupuncture on the function and pain in patients with acute LBP due to lumbosacral disc degeneration (LDD). Methods: One hundred and fifty-nine adults were randomly assigned to receive warm acupuncture treatment with silver needle (SvN) or with stainless steel needle (SSN) (1:1). Both groups received a 3-week therapy with 3 sessions per week. The primary outcome was the modified Oswestry Disability Index at week 4. The secondary outcomes included average pain, three physical sign tests and adverse events. Participants were followed up at week 16 and week 28 after randomization. Results: The LBP related disability and pain intensity significantly relieved more in the SvN warm acupuncture group than in the SSN group, in both the short and long term (p<0.001). The between-groups difference in physical signs showed statistical significance only in the short term (p = 0.024), but not in long term (p = 0.081; p = 0.069). Conclusion: Compared with warm acupuncture with stainless-steel needle at above 40°C, warm acupuncture with silver needle at above 43°C relieved more disability and pain in patients with acute LBP due to LDD. Study registration: Chinese Clinical Trial Registry (ChiCTR1800019051).

Temperature effect on seismic behavior of transmission tower-line system equipped with SMA-TMD

Li Tian,Juncai Liu,Canxing Qiu,Kunjie Rong 국제구조공학회 2019 Smart Structures and Systems, An International Jou Vol.24 No.1

Transmission tower-line system is one of most critical lifeline systems to cities. However, it is found that the transmission tower-line system is prone to be damaged by earthquakes in past decades. To mitigate seismic demands, this study introduces a tuned-mass damper (TMD) using superelastic shape memory alloy (SMA) spring for the system. In addition, considering the dynamic characteristics of both tower-line system and SMA are affected by temperature change. Particular attention is paid on the effect of temperature variation on seismic behavior. In doing so, the SMA-TMD is installed into the system, and its properties are optimized through parametric analyses. The considered temperature range is from -40 to 40°C. The seismic control effect of using SMA-TMD is investigated under the considered temperatures. Interested seismic performance indices include peak displacement and peak acceleration at the tower top and the height-wise deformation. Parametric analyses on seismic intensity and frequency ratio were carried out as well. This study indicates that the nonlinear behavior of SMA-TMD is critical to the control effect, and proper tuning before application is advisable. Seismic demand mitigation is always achieved in this wide temperature range, and the control effect is increased at high temperatures.

Evaluation of Conversion Action Data Mechanisms in Cost-Per-Action Advertising

Li Tian,Kyoung Jun Lee 한국경영정보학회 2008 한국경영정보학회 학술대회논문집 Vol.2008 No.-

Modal pushover analysis of self-centering concentrically braced frames

Li Tian,Canxing Qiu 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.65 No.3

Self-centering concentrically braced frames (SCCBFs) are emerging as high performance seismically resistant braced framing system, due to the capacity of withstanding strong earthquake attacks and promptly recovering after events. To get a further insight into the seismic performance of SCCBFs, systematical evaluations are currently conducted from the perspective of modal contributions. In this paper, the modal pushover analysis (MPA) approach is utilized to obtain the realistic seismic demands by summarizing the contribution of each single vibration mode. The MPA-based results are compared with the exact results from nonlinear response history analysis. The adopted SCCBFs originate from existing buckling-restrained braced frames (BRBF), which are also analyzed for purpose of comparison. In the analysis of these comparable framing systems, interested performance indices that closely relate to the structural damage degree include the interstory drift ratio, floor acceleration, and absorbed hysteretic energy. The study shows that the MPA approach produces acceptable predictions in comparison to the exact results for SCCBFs. In addition, the high-modes effect on the seismic behavior increases with the building height, and is more evident in the SCCBFs than the BRBFs.

중국 제조업 기업의 R&D 투자 및 수출 여부에 따른 생산성 분석

LI TIAN,이재민 한국무역연구원 2020 무역연구 Vol.16 No.4

Purpose We examine how the exports and R&D investments of individual firms in China affect their value added and analyze their relationship with total factor productivity (TFP). Design/Methodology/Approach This study uses panel data from China’s industrial enterprises for the period from 2005 to 2007, and in estimating es the production function using the two-step estimation method proposed by OP (1996) and constructs total factor productivity. In addition, using the concept of first-order stochastic advantage, total factor productivity is compared according to R&D investment and export status. Findings R&D investment is found to have a positive effect on value added, and export seems to have a limited positive effect on value added. We also find a positive relationship between R&D investment and productivity, and a limited positive relationship between export and productivity. Research Implications This analysis contributes to the research in that R&D investment and export have a positive effect on value added through sophisticated production function estimation. This study is very useful in that the TFP constructed through the estimation of the production function is compared using the nonparametric method. In addition, it has implications in that the importance of R&D investment is derived from empirical analysis, which has become a hot topic in recent years, in addition to traditional export issues in productivity.

Critical seismic incidence angle of transmission tower based on shaking table tests

Li Tian,Xu Dong,Haiyang Pan,Guodong Gao,Aiqiang Xin 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.76 No.2

Transmission tower-line systems have come to represent one of the most important infrastructures in today’s society. Recent strong earthquakes revealed that transmission tower-line systems are vulnerable to earthquake excitations, and that ground motions may arrive at such structures from any direction during an earthquake event. Considering these premises, this paper presents experimental and numerical studies on the dynamic responses of a 1000 kV ultrahigh-voltage (UHV) transmission tower-line system under different seismic incidence angles. Specifically, a 1:25 reduced-scale experimental prototype model is designed and manufactured, and a series of shaking table tests are carried out. The influence of the seismic incidence angle on the dynamic structural response is discussed based on the experimental data. Additionally, the incidence angles corresponding to the maximum peak displacement of the top of the tower relative to the ground (referred to herein as the critical seismic incidence angles) are summarized. The experimental results demonstrate that seismic incidence angle has a significant influence on the dynamic responses of transmission tower-line systems. Subsequently, an approximation method is employed to orient the critical seismic incidence angle, and a corresponding finite element (FE) analysis is carried out. The angles obtained from the approximation method are compared with those acquired from the numerical simulation and shaking table tests, and good agreement is observed. The results demonstrate that the approximation method can properly predict the critical seismic incidence angles of transmission tower-line systems. This research enriches the available experimental data and provides a simple and convenient method to assess the seismic performance of UHV transmission systems.

Research on vibration control of a transmission tower-line system using SMA-BTMD subjected to wind load

Li Tian,Jingyu Luo,Mengyao Zhou,Wenzhe Bi,Yuping Liu 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.82 No.5

As a vital component of power grids, long-span transmission tower-line systems are vulnerable to wind load excitation due to their high flexibility and low structural damping. Therefore, it is essential to reduce wind-induced responses of tower-line coupling systems to ensure their safe and reliable operation. To this end, a shape memory alloy-bidirectional tuned mass damper (SMA-BTMD) is proposed in this study to reduce wind-induced vibrations of long-span transmission tower-line systems. A 1220 m Songhua River long-span transmission system is selected as the primary structure and modeled using ANSYS software. The vibration suppression performance of an optimized SMA-BTMD attached to the transmission tower is evaluated and compared with the effects of a conventional bidirectional tuned mass damper. Furthermore, the impacts of frequency ratios and SMA composition on the vibration reduction performance of the SMA-BTMD are evaluated. The results show that the SMA-BTMD provides superior vibration control of the long-span transmission tower-line system. In addition, changes in frequency ratios and SMA composition have a substantial impact on the vibration suppression effects of the SMABTMD. This research can provide a reference for the practical engineering application of the SMA-BTMD developed in this study.

Seismic response control of transmission tower-line system using SMA-based TMD

Li Tian,Mengyao Zhou,Canxing Qiu,Haiyang Pan,Kunjie Rong 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.74 No.1

This study proposes a new shape memory alloy-tuned mass damper (SMA-TMD) and investigates the effectiveness of this damper in reducing and controlling the vibrations of a transmission tower-line system under various seismic excitations. Based on a practical transmission line system and considering the geometric nonlinearity of this system, the finite element (FE) software ANSYS is used to create an FE model of the transmission tower-line system and simulate the proposed SMA-TMD. Additionally, the parameters of the SMA springs are optimized. The effectiveness of a conventional TMD and the proposed SMA-TMD in reducing and controlling the vibrations of the transmission tower-line system under seismic excitations is investigated. Moreover, the effects of the ground motion intensity and frequency ratio on the reduction ratio (η) of the SMA-TMD are studied. The vibration reduction effect of the SMA-TMD under various seismic excitations is superior to that of the conventional TMD. Changes in the ground motion intensity and frequency ratio have a significant impact on the η of the SMA-TMD. As the ground motion intensity and frequency ratio increase, the η values of the SMA-TMD first increase and then decrease. Studying the vibration reduction effects of the SMA-TMD can provide a reference for the practical engineering application of this damper.

Seismic failure analysis and safety assessment of an extremely long-span transmission tower-line system

Li Tian,Haiyang Pan,Ruisheng Ma,Xu Dong 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.71 No.3

Extremely long-span transmission tower-line system is an indispensable portion of an electricity transmission system, and its failures or collapse can impact on the entire electricity grid, affect the modern life, and cause great economic losses. It is therefore imperative to investigate the failure and safety of the transmission tower subjected to ground motions. In the present study, a detailed finite element (FE) model of a representative extremely long-span transmission tower-line system is established. A segmental damage indicator (SDI) is proposed to quantitatively assess the damage level of each segment of the transmission tower under earthquakes. Additionally, parametric studies are conducted to investigate the influence of different ground motions and incident angles on the ultimate capacity and weakest segment of the transmission tower. Finally, the collapse fragility curve in terms of the maximum SDI value and PGA is plotted for the exampled transmission tower. The results show that the proposed SDI can quantitatively assess the damage level of the segments, and thus determine the ultimate capacity and weakest segment of the transmission tower. Moreover, the different ground motions and incident angles have a significant influence on the SDI values of the transmission tower, and the collapse fragility curve is utilized to evaluate the collapse resistant capacity of the transmission tower subjected to ground motions.