• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.21 no.3
• /
• pp.96-106
• /
• 2007

The terminal voltage of a synchronous generator is maintained by the field current control of excitation system. Generally AC/DC converter which is component of AVR(Automatic Voltage Regulator) system for excitation current control is connected to diode rectifier and DC/DC converter system. In the case of diode rectifier system of phase controlled converter as AC/DC converter have low power factor and harmonics of lower order in the line current. In this paper, two stage three phase PWM AC/DC converter is studied to solve these problems. The characteristics of a proposed converter reduces the harmonics and reactive power of the distribution line and has fast dynamic response in transient period using boost converter and current control mode buck converts. The proposed method is verified by the computer simulation and experimental results in prototype generation system.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.18 no.3
• /
• pp.331-339
• /
• 2016

Real time location (RTL) system which can control the safety of laborers in the underground space is developed in this study. This innovative system can monitor the location and history of movement of multiple laborers in real time. To accommodate constrains of the underground space, the system is portable and composed with low-battery mode. Since conventional method to detect the location of laborer with radio signal strength indicator (RSSI) contains high errors, new measurement system using accelerometers and correction method are suggested in this study. Field test is performed to validate the developed system. The error for moving laborer was 0.4 m and for non-moving laborers was 0.2 m. Thus, it is found that the new RTL system can be used to monitor the location of laborers in the underground construction space.

• Steel and Composite Structures
• /
• v.34 no.5
• /
• pp.643-655
• /
• 2020

In the present work, the buckling behavior of a single-layered graphene sheet (SLGS) embedded in visco-Pasternak's medium is studied using nonlocal four-unknown integral model. This model has a displacement field with integral terms which includes the effect of transverse shear deformation without using shear correction factors. The visco-Pasternak's medium is introduced by considering the damping effect to the classical foundation model which modeled by the linear Winkler's coefficient and Pasternak's (shear) foundation coefficient. The SLGS under consideration is subjected to compressive in- plane edge loads per unit length. The influences of many parameters such as nonlocal parameter, geometric ratio, the visco-Pasternak's coefficients, damping parameter, and mode numbers on the buckling response of the SLGSs are studied and discussed.

• Applied Biological Chemistry
• /
• v.29 no.4
• /
• pp.392-398
• /
• 1986

This study was conducted to find out the variation modes of the absorbtion contents of N, P and K and the contents of decursin, decursinol and sugar in Angelica gigas Nakai at different growth stages. The results of field study were as follows. The dried weights of root and shoot was increased by the application of nitrogen and potassium fertilizers during the growing seasons. But, the effect of phosphorus application was observed only the increasing of the dried weight of shoot. During the growing seasons, the contents of nitrogen and phosphorus in root was decreased, but in shoot was increased. The potassium contents of root was increased and that of shoot was decreased. The decursin and total sugar contents of root were continually increased, and the decursinol and reducing sugar contents were increased until the middle growth stage and after that were decreased.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.21 no.11
• /
• pp.2089-2094
• /
• 2017

Altmetrics is the measurement index and quantitative data to complement the traditional indicators based on the citation. Altmetrics research has acquired greater importance in the past few years, partly due to the complement to the traditional bibliometrics. This paper aims to reveal the research status and trends in altmetrics research. A total of 187 articles from 2005 to 2017 are obtained and analyzed, illustrating a steady rise (S-mode) in altmetrics research since 2005. Using social network analysis and co-word analysis, the author cooperation network and keyword co-occurrence network are developed. The core scientists and eight international research groups are discovered, reflecting that researchers in this field have a low degree of cooperation. Four topics of altmetrics research are discovered by hierarchical clustering. The results can be useful for the advanced research of altmetrics.

• Tunnel and Underground Space
• /
• v.16 no.6 s.65
• /
• pp.451-466
• /
• 2006

Analysis of slope behavior concerning the structural characteristics of field rock mass can be processed by virtue of borehole information of joint orientation and position acquired from DOM drilled core. Anticipated sliding potential of pre-failed rock slope is analyzed and the regional slope instability is investigated by inspecting the hazardous joints and blocks the traces of which is projected on the cut-face. Cross section has been set at the center of rock slope and the traces of both joints and tetrahedral blocks, which potentially can induce the slope failure, are drawn to investigate the failure modes and the triggering mechanism. Automated monitoring system has been established to measure the slope movement and especially, inclinometer has been installed inside DOM borehole to analyze the slope movement by considering the internal rock structure. Algorithms for predicting the slope failure time have been reviewed and the significance of heavy rainfall on the slope behavior has been investigated.

• Korean Journal of Bronchoesophagology
• /
• v.5 no.2
• /
• pp.153-158
• /
• 1999

Background and Objectives : The treatment of supraglottic stenosis remains a challenging problem in the field of otolaryngology due to its association with dyspnea, dysphagia, and frequent recurrence. Any satisfactory treatment is not yet known. The author experienced six cases of supraglottic stenosis and report the successful treatment of five cases by repeated endoscopic laryngeal excision with KTP-532 laser under suspension layngoscopy. Materials and Methods : Six adults who were treated for supraglottic stenosis between March 1994 and December 1998 at the Department of Otoloaryngology-Head and Neck Surgery, Korea University Medical Center were studied retrospectively. The patients were placed under general anesthesia followed by endoscopic laryngeal excision with KTP-532 laser under supension laryngoscopy. The scar tissue and granulation tissue were visualized with an operating microscope, and then removed using KTP-532 laser (15watts, continuous mode). Intraoperative local steroid(Triamcinolone ) was injected in all cases after the stenotic portions were removed. Results : Endoscopic excision was performed in five cases ; among the five cases, cricoid cartilage was concomitantly removed in two cases, and epiglottis was removed in one case. Satisfactory swallowing and airway respiration were possible in all five patients who underwent endoscopic widening. Conclusion : The treatment of supraglottic stenosis is different from that of tracheal or glottic stenosis in that supraglottic stenosis is mainly developed in membraneous form. Repeated laser excision and local steroid injection under suspension laryngoscopy is an effective and recommend able method for the treatment of supraglottic stenosis.

• Imaging Science in Dentistry
• /
• v.42 no.1
• /
• pp.19-24
• /
• 2012

Purpose : Field of view and voxel resolution of cone beam computed tomography (CBCT) might affect the diagnostic capability. This study was performed to compare between the standard and HiRes zoom modes in the diagnosis of external root resorption (ERR) using CBCT. Materials and Methods : Sixty three small cavities (0.25 mm depth and 0.5 mm diameter) were simulated on the buccal, lingual, and proximal surfaces at three different levels of 16 roots of teeth. After covering the root with nail varnish, the roots were inserted in the sockets and the model was placed in a water-containing lacuna. CBCT scans were taken in both standard and HiRes zoom modes using NewTom VG (QR srl Company, Verona, Italy). Then, an observer assessed the images to determine the presence or absence of the cavities. This process was repeated by increasing the size and depth of cavities to 0.5 mm depth and 1 mm diameter. Data were analyzed by McNemar test. The sensitivity, specificity, positive predictive value, negative predictive value, and likelihood ratio in evaluation of the simulated cavities were calculated. Results : There was a significant difference between the two imaging modes in diagnosing the shallow cavities (p=0.02).The sensitivity of the standard zoom in detecting the shallow cavities was lower than that of the HiRes zoom. The likelihood ratio of the HiRes zoom was higher in the diagnosis of both cavity types. Conclusion : This study suggested that a smaller voxel size in the HiRes zoom mode of CBCT is preferred for diagnosis of ERR.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.14 no.2
• /
• pp.57-65
• /
• 2010

To determine the static buckling loads and evaluate the structural performance of slender steel pipe-arches such as for greenhouse structures, a series of modal tests using a fixed hammer and roving sensors was carried out, by providing no load, then a range of vertical loads, on an arch rib in several steps. More attention was given to an internal arch where vertical and horizontal auxiliary members are not placed, unlike an end arch. Modal parameters such as natural frequencies, mode shapes and damping ratios were extracted using more advanced system identification methods such as PolyMAX (Polyreference Least-Squares Complex Frequency Domain), and compared with those predicted by commercial FEA (Finite Element Analysis) software ANSYS for various conditions. A good correlation between them was achieved in an overall sense, however the reduction of natural frequencies due to the existence of preaxial loads was not apparent when the vertical load level was about up to 38% of its resistance. Some difficulties related to the field testing and parameter extraction for a very slender arch, as might arise from the influences of neighboring members, are carefully discussed.

• Journal of the Korean Institute of Telematics and Electronics D
• /
• v.36D no.7
• /
• pp.42-49
• /
• 1999

In this paper, we proposed a simple measurement method to find the behaviors of the fiber-to-waveguide coupler. The polished fiber blocks and planar waveguides on silicon dioxide were fabricated independently and then optically coupled by physical pressure. Several kinds of polymer with different refractive indices were used for waveguide films. The proposed method makes it possible to measure the center wavelength, bandwidth, extinction ratio, and polarization dependence of the coupler during fabrication procedure. The wavelength sensitivity increased with refractive index of polymer. The symmetric planar waveguide structure and isotropic property of guiding materials reduced polarization dependent property. Insertion loss of the coupler was less than 0.5dB. It is expected that our measurement method is useful for developing various optical devices using evanescent coupling between polished fiber and planar waveguide such as optical modulators and filters etc.