• Structural Engineering and Mechanics
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• 제77권5호
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• pp.601-612
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• 2021

To study the vibration characteristics of a high-speed railway continuous girder bridge-track coupling system (HSRCBT), a coupling vibration analysis model of an m-span continuous girder bridge-subgrade-track system with n-span approach bridge was established. The model was based on the energy and its variational method, where both the interlaminar slip and shear deformation effects were considered. In addition, the free vibration equations and natural boundary conditions of the HSRCBT were derived. Further, according to the coordination principle of deformation and mechanics, an analytical method for calculating the natural vibration frequencies of the HSRCBT was obtained. Three typical bridge-subgrade-track coupling systems of high-speed railway were taken and the results of finite element analysis were compared to those of the analytical method. The errors between the simulation results and calculated values of the analytical method were less than 3%, thus verifying the analytical method proposed in this paper. Finally, the analytical method was used to investigate the influence of the number of the approach bridge spans and the interlaminar stiffness on the natural vibration characteristics of the HSRCBT based on the degree of sensitivity. The results suggest the approach bridges have a critical number of spans and in general, the precision requirements of the analysis could be met by using 6-span approach bridges. The interlaminar vertical compressive stiffness has very little influence on the low-order natural vibration frequency of HSRCBT, but does have a significant influence on higher-order natural vibration frequency. As the interlaminar vertical compressive stiffness increases, the degree of sensitivity to interlaminar stiffness of each of the HSRCBT natural vibration characteristics decrease and gradually approach zero.

• Structural Engineering and Mechanics
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• 제83권2호
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• pp.207-227
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• 2022

In general, the interaction conditions between the discrete stones are not taken into account by structural engineers during the modeling and analyzing of historical stone bridges. However, many structural damages in the stone bridges occur due to ignoring the interaction conditions between discrete stones. In this study, it is aimed to examine the seismic behavior of a historical stone bridge by considering the interaction stiffness parameters between stone elements. For this purpose, Tokatli historical stone arch bridge was built in 1179 in Karabük-Turkey, is chosen for three-dimensional (3D) seismic analyses. Firstly, the 3D finite-difference model of the Tokatli stone bridge is created using the FLAC3D software. During the modeling processes, the Burger-Creep material model which was not used to examine the seismic behavior of historical stone bridges in the past is utilized. Furthermore, the free-field and quiet non-reflecting boundary conditions are defined to the lateral and bottom boundaries of the bridge. Thanks to these boundary conditions, earthquake waves do not reflect in the 3D model. After each stone element is modeled separately, stiffness elements are defined between the stone elements. Three situations of the stiffness elements are considered in the seismic analyses; a) for only normal direction b) for only shear direction c) for both normal and shear directions. The earthquake analyses of the bridge are performed for these three different situations of the bridge. The far-fault and near-fault conditions of 1989 Loma Prieta earthquake are taken into account during the earthquake analyses. According to the seismic analysis results, the directions of the stiffness parameters seriously changed the earthquake behavior of the Tokatli bridge. Moreover, the most critical stiffness parameter is determined for seismic analyses of historical stone arch bridges.

• Structural Engineering and Mechanics
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• 제83권5호
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• pp.693-707
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• 2022

Bonded joints have proven their performance against conventional joining processes such as welding, riveting and bolting. The single-lap joint is the most widely used to characterize adhesive joints in tensile-shear loadings. However, the high stress concentrations in the adhesive joint due to the non-linearity of the applied loads generate a bending moment in the joint, resulting in high stresses at the adhesive edges. Geometric optimization of the bonded joint to reduce this high stress concentration prompted various researchers to perform geometric modifications of the adhesive and adherends at their free edges. Modifying both edges of the adhesive (spew) and the adherends (bevel) has proven to be an effective solution to reduce stresses at both edges and improve stress transfer at the inner part of the adhesive layer. The majority of research aimed at improving the geometry of the plate and adhesive edges has not considered the effect of temperature and water absorption in evaluating the strength of the joint. The objective of this work is to analyze, by the finite element method, the stress distribution in an adhesive joint between two 2024-T3 aluminum plates. The effects of the adhesive fillet and adherend bevel on the bonded joint stresses were taken into account. On the other hand, degradation of the mechanical properties of the adhesive following its exposure to moisture and temperature was found. The results clearly showed that the modification of the edges of the adhesive and of the bonding agent have an important role in the durability of the bond. Although the modification of the adhesive and bonding edges significantly improves the joint strength, the simultaneous exposure of the joint to temperature and moisture generates high stress concentrations in the adhesive joint that, in most cases, can easily reach the failure point of the material even at low applied stresses.

• Structural Engineering and Mechanics
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• 제84권5호
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• pp.619-632
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• 2022

Reinforced concrete (RC) structures may be subjected to sudden dynamic impact loads such as explosions occurring for different reasons, the collision of masses driven by rockfall, flood, landslide, and avalanche effect structural members, the crash of vehicles to the highway and seaway structures. Many analytical, numerical, and experimental studies focused on the behavior of RC structural elements such as columns, beams, and slabs under sudden dynamic impact loads. However, there is no comprehensive study on the behavior of the RC column-beam connections under the effect of sudden dynamic impact loads. For this purpose, an experimental study was performed to investigate the behavior of RC column-beam connections under the effect of low-velocity impact loads. Sixteen RC beam-column connections with a scale of 1/3 were manufactured and tested under impact load using the drop-weight test setup. The concrete compressive strength, shear reinforcement spacing in the beam, and input impact energy applied to test specimens were taken as experimental variables. The time histories of impact load acting on test specimens, accelerations, and displacements measured from the test specimens were recorded in experiments. Besides, shear and bending crack widths were measured. The effect of experimental variables on the impact behavior of RC beam-column connections has been determined and interpreted in detail. Besides, a finite element model has been established for verification and comparison of the experimental results by using ABAQUS software. It has been demonstrated that concrete strength, shear reinforcement ratio, and impact energy significantly affect the impact behavior of RC column-beam connections.

• 디자인융복합연구
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• 제17권3호
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• pp.1-19
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• 2018

수부재활훈련도구는 저하된 수부 기능 회복 및 전체적인 수부 기능 향상을 필요로 하는 환자와 사용자들을 위해 병원 및 가정에서 치료와 함께 병행한다. 이에 따라 다양한 목적의 수부재활훈련도구의 개발 또한 함께 이루어 지고 있으며, 많은 도구가 보급되어 각 병원에서 규정한 프로세스로 재활훈련을 진행하고 있다. 그러나 현재 병원에서 활용하는 훈련도구들은 점진적인 시스템으로 구성되어 있지 않고 일정 시간동안 단순반복성 동작을 유도한다. 따라서 재활훈련을 하는 환자들이 무료함을 느끼며 재활에 대한 동기부여를 갖지 못하므로 지속적이고 효과적인 훈련이 어렵다. 또한, 훈련에 활용되는 도구들은 고가인 경우가 대부분이며, 공간적 제한성으로 인해 환자의 자발적 재활훈련을 어렵게 한다. 이는 환자의 경제적 부담을 가중시킴과 동시에 올바른 신체적 향상을 가져오지 못하는 문제로 이어질 수 있다. 이러한 논점을 바탕으로 본 연구는 놀이요소 중 하나인 실뜨기를 접목해 과제를 통한 효과적 재활훈련이 이루어질 수 있도록 하고, 경제적이며 자유로운 재활이 이루어질 수 있도록 하고자 한다. 이를 위해 도구의 특성과 사용자 환경을 조사한 후 실뜨기 놀이와, 훈련도구와의 관련성 및 지속적인 재활이 가능한지에 대한 타당성을 확인하고 전문가 인터뷰를 통해 디자인 요소를 도출하였다. 이후 디자인 가이드라인 및 프로토타입을 제작해 사용성 테스트 및 디자인요소 평가를 진행하여 문제점을 보완하였다.

• The Journal of Advanced Prosthodontics
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• 제16권2호
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• pp.77-90
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• 2024

PURPOSE. The study aims to investigate the influence of the ferrule effect and types of posts on the stress distribution in three morphological types of the maxillary central incisor. MATERIALS AND METHODS. Nine models were created for 3 maxillary central incisor morphology types: "Fat" type - crown 12.5 mm, root 13 mm, and buccolingual cervical diameter 7.5 mm, "Medium" type - crown 11 mm, root 14 mm, and buccolingual cervical diameter 6.5 mm, and "Slim" type - crown 9.5 mm, root 15 mm, and buccolingual cervical diameter 5.5 mm. Each model received an anatomical castable post-and-core or glass-fiber post with resin composite core and three ferrule heights (nonexistent, 1 mm, and 2 mm). Then, a load of 14 N was applied at the cingulum with a 45° slope to the long axis of the tooth. The Maximum Principal Stress and the Minimum Principal Stress were calculated in the root dentin, crown, and core. RESULTS. Higher tensile and compression stress values were observed in root dentin using the metallic post compared to the fiber post, being higher in the slim type maxillary central incisor than in the medium and fat types. Concerning the three anatomical types of maxillary central incisors, the slim type without ferrule height in mm presented the highest tensile stress in the dentin, for both types of metal and fiber posts. CONCLUSION. Post system and tooth morphology were able to modify the biomechanical response of restored endodontically-treated incisors, showing the importance of personalized dental treatment for each case.

• Structural Engineering and Mechanics
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• 제90권4호
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• pp.325-343
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• 2024

Triple-tower double-cable suspension bridges have increased confinement stiffness imposed by the main cable on the middle tower, which has bright application prospects. However, vertical bending and torsional vibrations of the double-cable and the girder are coupled in such bridges due to the hangers. In particular, the bending vibration of the towers in the longitudinal direction and torsional vibrations about the vertical axis influence the vertical bending and torsional vibrations of the stiffening girders, respectively. The conventional analytical algorithm for assessing the dynamic features of the suspension bridge is not directly applicable to this type of bridge. This study attempts to mitigate this problem by introducing an analytical algorithm for solving the triple-tower double-cable suspension bridge's natural frequencies and mode shapes. D'Alembert's principle is employed to construct the differential equations of the vertical bending and torsional vibrations of the stiffening girder continuum in each span. Vibrations of stiffening girders in each span are interrelated via the vibrations of the main cables and the bridge towers. On this basis, the natural frequencies and mode shapes are derived by separating variables. The proposed algorithm is then applied to an engineering example. The natural frequencies and mode shapes of vertical bending and torsional vibrations derived by the analytical algorithm agreed well with calculations via the finite element method. The fundamental frequency of vertical bending and first- and second-order torsion frequencies of double-cable suspension bridges are much higher than those of single-cable suspension bridges. The analytical algorithm has high computational efficiency and calculation accuracy, which can provide a reference for selecting appropriate structural parameters to meet the requirements of dynamics during the preliminary design.

• Applied Microscopy
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• 제30권4호
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• pp.347-355
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• 2000

Zinc는 인체 내에 철$(Fe^{2+})$다음으로 많은 trace element로서 200여개 효소의 기능에 필수적일 뿐만 아니라 신경계통내에서는 신경조절물질로 작용한다. 뿐만 아니라 허혈, 간질 및 퇴행성 뇌질환의 주요 병리기전에도 관여되어 있다. 그러나 대부분의 Zinc는 단백질에 결합되어 (bound form)신경세포의 세포질 및 핵질내에 존재하고, 10% 이하의 Zinc는 이온상태(free form, $Zn^{2+}$)로 신경종말 (Zinc enriched terminal)에 있는데 , 후자만이 조직화학법으로 가시화된다. 최근까지 새로 개발된 조직화학법으로 Zinc enriched(ZEN)neurons의 분포에 관한 연구가 각광받고 있으나, 국내에서는 이에 대한 연구가 전무한 실정이다. 이에 본 연구자는 고전적인 조직화학법의 기본 원리를 소개하고, 렛드 중추신경계통내 Zinc의 분포를 광학 및 전자현미경으로 관찰하고자 하였다. 본 연구에서 사용된 실험동물은 Wistar 계통의 랫드(10주령)와 BALB/c 마우스이며, 마취제로는 Pentobarbital(50mg/kg)을 이용하였다. 생체 뇌조직내 이온상태의 $Zinc(Zn^{2+})$를 침전시키기 위하여 selenium(10mg/kg, i.p.)을 처리하였고, 1시간 후 3% Glutaraldehyde액으로 관류고정하여 동물을 희생시켰다. 뇌와 척수를 꺼내어 sucrose에 가라앉을때 까지 담가두었다가 Dry Ice를 이용하여 얼리고, Freezing microtome위에서 $30{\mu}m$두께의 절편을 작성하였다. 조직절편내 $Zn^{2+}$을 동정하기 위한 조직화학법으로는 autometallography (AMG) (Danscher, 1985)를 이용하였다. 광학현미경하에서 밝혀진 Zinc의 분포는 해마복합체를 비롯한 종뇌의 여러부위에 고농도로 분포하였고, 척수에는 중간정도, 그리고 소뇌 및 뇌간에는 매우 낮은 농도로 분포하였다. 전자현미경에서 관찰된 AMG염색과립(silver grains)은 신경종말에 있는 연접소포에 국한되었으며, 이러한 ZEN terminals은 주위 여러 신경세포의 돌기(dendrites)및 세포체 (soma)에 특이한 연접을 이루고 있었다. 즉 후각망울을 포함한 종뇌에서는 주로 비대칭연접 (asymmetrical synapses)이 관찰되었던 반면에, 척수에서는 대칭연접(symmetrical synapses)을 이루고 있었다. 이상의 결과를 종합하면, 신경종말내 연접소포에 Zinc를 함유하고 있는 소위 ZEN terminals은 중추신경계통에 광범위하게 분포하고 있으며 또한 신경부위에 따라 다양한 분포와 미세구조의 차이를 보였다. 이러한 사실은 중추신경계통내에서 Zinc가 영위하는 신경생물학적 기능이 신경부위에 따라 다양할 것임을 시사한다.

• 한국자원식물학회지
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• 제9권3호
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• pp.230-238
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• 1996

재배장소(栽培場所)에 따른 야생(野生)더덕 및 재배(栽培)더덕의 기상환경(氣象環境), 생육특성(生育特性), 일반성분(一般成分), 유리(遊離) 아미노산(酸) 및 식물성(植物性) 정유성분(精油成分)을 비교분석(比較分析)한 결과(結果)를 요약(要約)하면 다음과 같다. 1. 자생지(自生地)는 재배지(栽培地에)에 비하여 기온(氣溫)이 $2{\sim}3^{\circ}C$ 지온(地溫)은 $2^{\circ}C$ 정도(程度)로 낮았고 조도(照度) 량(量낮)은 재배지(栽培地)의 2.9%였다. 자생지(自生地) 토양(土壤)의 pH는 재배지(栽培地)보다 다소 낮았으며 유기물(有機物) 함량(含量)은 4.8%로 1.7배(倍) 정도 높게 나타났다. 2. 자생지(自生地) 재배(栽培)더덕의 개화기(開花期)가 8월(月)3일(日)로 같았지만 재배지(栽培地) 야생(野生)더덕은 재배(栽培) 더덕 보다 10일(日) 늦은 8월(月)15일(日)이었다. 만장(蔓長), 엽장(葉長), 경경(莖徑) 등(等)은 재배(栽培) 장소(場所)와는 무관(無關)하게 야생(野生)더덕에서 저조(低調)하였으나 방향성(芳香性)은 평균(平均) 5로서 재배(栽培)더덕이 평균(平均) 3.5인 것에 비해 높은 것으로 나타났다. 3. 야생(野生)더덕의 생체중(生體重)은 평균(平均) 11g/주(株)인 것에 비하여 재배(栽培)더덕은 23.5g/주(株딘)였으나 방향성(芳香性)은 재배지(栽培地)에서는 차이(差異)가 없었으나 자생지(自生地)에서는 야생(野生)더덕이 5 정도(程度)로 다소 높은 경향(傾向)을 보였다. 4. 야생(野生)더덕과 재배(栽培)더덕의 재배장소별(栽培場所別) 일반성분(一般性分)의 조성(組成)은 조단백질(粗蛋白質)의 경우(境遇) 재배장소(栽培場所)에 따른 차이(差異)를 보였으며 자생지(自生地)보다 재배지(栽培地)에서 높은 함량(含量)을 보였고 조(粗)사포닌은 재배지(栽培地)보다 자생지(自生地)에서 높은 함량(含量)을 보였다. 5. 무기성분함양(無機成分含量)의 차이(差異)는 K의 경우(境遇) 자생지(自生地)에서 보다 재배지(栽培地)에서 평균적(平均的)으로 10배이상(倍以上) 정도(程度) 높은 함량(含量)의 차이(差異)를 보였으나 Mn, Zn, Na, Cu 등(等)은 일정(一定)한 경향(傾向)을 보이지 않는 것으로 나타났다. 6. 유리(遊離) 아미노산(酸)의 함량(含量)은 자생지(自生地은)보다 재배지(栽培地)에서 전반적(全般的)으로 높은 함량(含量)을 나타내었고, 특(特)히 Arginine은 다른 성분(成分)들과 비교(比較)해 볼 때 가장 높은 조성(組成)의 차이(差異)를 나타내었다. 7. 야생(野生)더덕과 재배(栽培)더덕의 정유성분수율(精油成分收率)은 자생지재배(自生地栽培)에서는 모두 0.004% 였고 재배지(栽培地)에서는 야생(野生)더덕이 0.005%였다. 8. 더덕의 재배장소(栽培場所)에 따른 향기성분(香氣成分)은 총(總) 21종(種)이었으며 自生地(自生地)에서 야생(野生)더덕은 16종(種), 재배(栽培)더덕은 18종(種)이었고, 재배지(栽培地)에서 야생(野生) 더덕은 14종(種), 재배(栽培)더덕은 20(種)이었다. 9. Trans-2-hexanol은 야생(野生)더덕의 자생지(自生地) 재배(栽培)에서 피이크 면적(面積) 당(當) 50.3%, 재배지(栽培地)에서 피이크 면적(面積) 당(當) 43.3%를 보였으며 amylalcohol, furfuryl acetate, 2-methoxy-4-vinyl phenol(MVP)는 재배(栽培)더덕에서만 확인(確認)되었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.115-116
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• 2012

The demand for flexible electronic systems such as wearable computers, E-paper, and flexible displays has increased due to their advantages of excellent portability, conformal contact with curved surfaces, light weight, and human friendly interfaces over present rigid electronic systems. This seminar introduces three recent progresses that can extend the application of high performance flexible inorganic electronics. The first part of this seminar will introduce a RRAM with a one transistor-one memristor (1T-1M) arrays on flexible substrates. Flexible memory is an essential part of electronics for data processing, storage, and radio frequency (RF) communication and thus a key element to realize such flexible electronic systems. Although several emerging memory technologies, including resistive switching memory, have been proposed, the cell-to-cell interference issue has to be overcome for flexible and high performance nonvolatile memory applications. The cell-to-cell interference between neighbouring memory cells occurs due to leakage current paths through adjacent low resistance state cells and induces not only unnecessary power consumption but also a misreading problem, a fatal obstacle in memory operation. To fabricate a fully functional flexible memory and prevent these unwanted effects, we integrated high performance flexible single crystal silicon transistors with an amorphous titanium oxide (a-TiO2) based memristor to control the logic state of memory. The $8{\times}8$ NOR type 1T-1M RRAM demonstrated the first random access memory operation on flexible substrates by controlling each memory unit cell independently. The second part of the seminar will discuss the flexible GaN LED on LCP substrates for implantable biosensor. Inorganic III-V light emitting diodes (LEDs) have superior characteristics, such as long-term stability, high efficiency, and strong brightness compared to conventional incandescent lamps and OLED. However, due to the brittle property of bulk inorganic semiconductor materials, III-V LED limits its applications in the field of high performance flexible electronics. This seminar introduces the first flexible and implantable GaN LED on plastic substrates that is transferred from bulk GaN on Si substrates. The superb properties of the flexible GaN thin film in terms of its wide band gap and high efficiency enable the dramatic extension of not only consumer electronic applications but also the biosensing scale. The flexible white LEDs are demonstrated for the feasibility of using a white light source for future flexible BLU devices. Finally a water-resist and a biocompatible PTFE-coated flexible LED biosensor can detect PSA at a detection limit of 1 ng/mL. These results show that the nitride-based flexible LED can be used as the future flexible display technology and a type of implantable LED biosensor for a therapy tool. The final part of this seminar will introduce a highly efficient and printable BaTiO3 thin film nanogenerator on plastic substrates. Energy harvesting technologies converting external biomechanical energy sources (such as heart beat, blood flow, muscle stretching and animal movements) into electrical energy is recently a highly demanding issue in the materials science community. Herein, we describe procedure suitable for generating and printing a lead-free microstructured BaTiO3 thin film nanogenerator on plastic substrates to overcome limitations appeared in conventional flexible ferroelectric devices. Flexible BaTiO3 thin film nanogenerator was fabricated and the piezoelectric properties and mechanically stability of ferroelectric devices were characterized. From the results, we demonstrate the highly efficient and stable performance of BaTiO3 thin film nanogenerator.