Sung-Kyung Lee

Increased striatal dopamine transporter density in moderately severe old restless legs syndrome patients.

Background and purpose:  Dopamine dysregulation in restless legs syndrome (RLS) may be varied by the severity of RLS, which could contribute to the conflicting results from previous functional neuroimaging studies on the central dopaminergic neurotransmission of RLS. The aim of this study was to observe whether reduced striatal dopaminergic neurotransmission is associated with moderate to moderately severe RLS.

Availability of brain serotonin transporters in patients with restless legs syndrome

Background: Selective serotonin reuptake inhibitors have been associated with the risk of restless legs syndrome (RLS), suggesting that dysregulation of serotonergic neurotransmission may provoke or exacerbate RLS. Methods: We compared the availability of serotonin transporter (SERT) between 16 drug-naïve patients with RLS and 16 healthy controls. SERT was measured in the pons and medulla via [123I]-2β-carbomethoxy-3β-(4-iodophenyl) tropane (β-CIT) SPECT. A ratio of specific to nonspecific brain uptake (V3″) was used for all comparisons. RLS was diagnosed according to the criteria proposed by the National Institute of Health, and its severity was measured using the International RLS Study Group (IRLSSG) Severity Scale. Results: The availability of SERT was similar in the RLS group and the control group with regards to the pons (1.24 ± 0.31 vs 1.24 ± 0.25, p > 0.1) and the medulla (0.99 ± 0.25 vs 1.00 ± 0.23, p > 0.1). However, IRLSSG Severity Scale scores increased with decrease of SERT availability in both the pons (β = −0.50, t = −3.19, p = 0.009) and the medulla (β = −0.42, t = −2.44, p = 0.03). Conclusions: Although serotonin transporter (SERT) availability in pons and medulla was similar in the restless legs syndrome (RLS) group and the control group, the severity of RLS symptoms increased as the availability of SERT decreased. These data partially support the hypothesis that an increase of serotonergic neurotransmission in the brainstem may exacerbate RLS, possibly via dual modulations on striatal dopaminergic neurotransmission and on the activities of spinal motor and sensory neurons.

Experimental implementation of a building structure with a tuned liquid column damper based on the real-time hybrid testing method

In this study, the real-time hybrid test using a shaking table for the control performance evaluation of a U-shaped tuned liquid column damper (TLCD) controlling the response of earthquake-excited building structure is experimenttally implemented. In the test, the building structure is used as a numerical part, on which a U-shaped TLCD adopted as an experimental part was installed to reduce its response. At first, the force that is acting between a TLCD and building structure is measured from the load cell attached on shaking table and is fed-back to the computer to control the motion of shaking table. Then, the shaking table is driven such a manner that the error between the interface acceleration computed from the numerical building structure under the excitations of earthquake and the fed-back interface force and that measured from the shaking table. The control efficiency of the TLCD used in this paper is experimentally confirmed by implementing this process of shaking table experiment on real-time.

Experimental Investigation of MR Damper-based Semiactive Control Algorithms for Full-scale Five-story Steel Frame Building

In this study, the effectiveness of various semiactive control algorithms based on magnetorheological (MR) dampers is experimentally investigated for seismic protection of a full-scale five-story steel frame building structure. This may be the first experimental comparison of several semiactive control algorithms using a full-scale test structure. The MR damper-based control systems are realized, when an MR damper is designed by deriving a suboptimal design procedure considering optimization problem and magnetic analysis, and then a damper with the capacity of 1.0 ton is manufactured. In the experiments, a linear active mass driver and the linear shaker seismic simulation testing method are used to excite the building structure in order to match the full-scale building vibrate as if the building undergoes an earthquake. Under the four historical earthquakes and one filtered artificial earthquake, the performance of the semiactive control algorithms including the passive optimal case is experimentally evaluated. From the experimental results, one can conclude that the Lyapunov and semiactive neuro-control algorithms are appropriate in reducing accelerations of the structural system, and the passive optimal case and the maximum energy dissipation algorithm show the excellent performance in reducing the first floor displacement.

Real-time Hybrid Test on a Semi-actively Controlled Building Structure Equipped with Full-scale MR Dampers

The real-time hybrid testing method (RT-HYTEM) is a structural testing technique in which the numerical integration of the equation of motion for a numerical substructure and the physical testing for an experimental substructure are performed simultaneously in real-time. This article presents the quantitative evaluation of the seismic performance of a building structure installed with a magnetorheological (MR) damper using RT-HYTEM. A building model is identified from the force-vibration testing results of a full-scale five-story building and is used as the numerical substructure, and an MR damper corresponding to an experimental substructure is physically tested using a universal testing machine (UTM). First, the force required to drive the displacement of the story, at which the MR damper is located, is measured from the load cell attached to the UTM. The measured force is then returned to a control computer to calculate the response of the numerical substructure. Finally, the experimental substructure is excited by the UTM with the calculated response of the numerical substructure. The RT-HYTEM implemented in this study is validated because the real-time hybrid testing results obtained by application of sinusoidal and earthquake excitations and the corresponding analytical results obtained using the Bouc-Wen model as the control force of the MR damper with respect to input currents are in good agreement. Also, the results from RT-HYTEM for the passive -on and -off control show that the structural responses did not decrease further by the excessive control force, but decreased due to the increase of the current applied to the MR damper. Also, two semi-active control algorithms (modulated homogeneous friction and the clipped-optimal control algorithms) are applied to the MR damper in order to optimally control the structural responses. To compare the RT-HYTEM and numerical results, Bouc-Wen model parameters are identified for each input current. The results of the comparison of experimental and numerical responses show that it is more practical to use RT-HYTEM in semi-active devices such as MR dampers. The test results show that a control algorithm can be experimentally applied to the MR damper using RT-HYTEM. This article provides a discussion on each algorithm with respect to the seismic performances.

Bracing Systems for Installation of MR Dampers in a Building Structure

In this study, the effects of bracing systems for installing a magnetorheological (MR) damper in a building structure on seismic response control are analytically and experimentally investigated. The performance of the toggle brace system which enables the installed damper to generate larger effective control force due to its response amplification mechanism than a conventional brace system is evaluated. In addition, the nonlinear velocity amplification factor for the toggle brace—MR damper system and the effect of toggle configuration are considered. Analytical and experimental results show that control performance can be enhanced using the toggle brace system especially for the case in which the MR damper installed using non-amplifying brace system cannot provide sufficient response reduction.

A Tuned Liquid Mass Damper(TLMD) for Controlling Bi-directional Responses of a Building Structure

This paper presents a design of a tuned liquid mass damper(TLMD) for controlling bi-directional response of high-rise building structure subjected to windload. The proposed damper behaves as a tuned mass damper(TMD) of which mass is regarded as the mass of a tuned liquid column damper(TLCD) and the case wall of the TLCD itself in one direction and the TLCD in the other direction. Because the proposed device has coupled design parameter along two orthogonal directions, it is very important to select designing components by optimal fine tuning. In the designing TLMD, for easy maintenance, the rubber-bearing with small springs was applied in TMD direction. In this study, the Songdo New City Tower 1A in Korea, which has been designed and constructed two TLCDs in order to control bi-directional response, was chosen as the model building structure. The results of rotation test proved the effectiveness of bi-directional behavior of TLMD.

Real-Time Hybrid Testing of a Steel-Structure Equipped With Large-Scale Magneto-Rheological Dampers Applying Semi-Active Control Algorithms

This study introduces the quantitative evaluation of the seismic performance of a building structure equipped with MR dampers by using real-time hybrid testing method (RT-HYTEM). A real-scaled 5-story building is used as the numerical substructure, and MR dampers corresponding to an experimental substructure is physically tested by using UTM. First, the force required to drive the displacement of the story, at which the MR damper is located, is measured from the load cell attached to UTM. Then, the measured force is returned to a control computer to calculate the response of the numerical substructure. Finally, the experimental substructure is excited by UTM with the calculated response of the numerical substructure. The RT-HYTEM implemented in this study is validated for that the real-time hybrid testing results obtained by application of sinusoidal and earthquake excitations and the corresponding analytical results obtained by using the Bouc-Wen model as the control force of the MR damper respect to input currents were in good agreement. Furthermore, semi-active control algorithms were applied to the MR damper. The comparison results of experimental and numerical responses demonstrated that using RT-HYTEM was more reasonable in semi-active devices such as MR dampers having strong nonlinearity.Copyright

Performance evaluation of passive and semi-active magnetorheological dampers

Seismic control performance of the magnetorheological (MR) damper, which has strong nonlinearity, varies with the dynamic characteristics of the structure and ground motion such as natural period, peak ground acceleration. The MR damper has a property of the friction damper so that the relative magnitude of the friction force over excitation intensity affects the control performance. In this study, through numerical analyses of single-degree-of-freedom (SDOF) structures, design spectra for the passive MR damper and optimal non-dimensional friction forces are suggested. Additionally, simple semi-active control algorithms modulating the friction force of the MR damper in accordance with structural responses are proposed and compared with each other and the passive MR damper. Finally, the condition that the semi-active control is more appropriate than the passive one is identified for reasonable selection of the control strategy.

Investigation on Vibration Characteristics and Structural Reciprocity of Heunginjimun

Heunginjimun designated as a Treasure No.1 is a two-story wooden structure with 5 bay and 2 bay in its front and side views, respectively. This paper presents an investigation on vibration characteristics of Heunginjimun through both ambient vibration and impact hammer tests. Ambient vibration test was performed to identify the natural frequency of Heunginjimun from the spectrum analysis of time history. Impact hammer test was undertaken to find the frequency of Heunginjimun which is affected by the surrounding traffics and to verify the reciprocal principle for the wooden structural system. Ambient vibration test results of Heunginjimun showed that the natural frequencies in two principal axes 1.5 Hz and 1.1 Hz, respectively. It was confirmed from impact hammer tests for a ground that the frequency of 4.2 Hz is caused by the traffics surrounding Heunginjimun. It was also observed that from the impact hammer test results between two locations in Heunginjimun that the transfer functions measured from two corresponding locations coincided well with each other. This result shows that the wooden structural system is globally linear, and the reciprocal principle is established.Heunginjimun designated as a Treasure No.1 is a two-story wooden structure with 5 bay and 2 bay in its front and side views, respectively. This paper presents an investigation on vibration characteristics of Heunginjimun through both ambient vibration and impact hammer tests. Ambient vibration test was performed to identify the natural frequency of Heunginjimun from the spectrum analysis of time history. Impact hammer test was undertaken to find the frequency of Heunginjimun which is affected by the surrounding traffics and to verify the reciprocal principle for the wooden structural system. Ambient vibration test results of Heunginjimun showed that the natural frequencies in two principal axes 1.5 Hz and 1.1 Hz, respectively. It was confirmed from impact hammer tests for a ground that the frequency of 4.2 Hz is caused by the traffics surrounding Heunginjimun. It was also observed that from the impact hammer test results between two locations in Heunginjimun that the transfer functions measured from two corresponding locations coincided well with each other. This result shows that the wooden structural system is globally linear, and the reciprocal principle is established.