Scalable assembly method of vertically-suspended and stretched carbon nanotube network devices for nanoscale electro-mechanical sensing components.

Lee, Ung Yang,Heo, Kwang,Bak, Jung Hoon,Cho, Sung Un,Moon, Seungeon,Park, Yun Daniel,Hong, Seunghun American Chemical Society 2008 NANO LETTERS Vol.8 No.12

<P>For the first time, vertically suspended and stretched carbon nanotube network junctions were fabricated in large quantity via the directed assembly strategy using only conventional microfabrication facilities. In this process, surface molecular patterns on the side-wall of the Al structures were utilized to guide the assembly and alignment of carbon nanotubes in the solution. We also performed extensive experimental (electrical and mechanical) analysis and theoretical simulation about the vertically suspended single-walled carbon nanotube network junctions. The junctions exhibited semiconductor-like conductance behavior. Furthermore, we demonstrated gas sensing and electromechanical sensing using these devices.</P>

RANS based CFD simulations for urban wind prediction field verification against MoTUS

Daniel Sang-Hoon Lee,Dasaraden Mauree 한국풍공학회 2021 Wind and Structures, An International Journal (WAS Vol.33 No.1

The current paper presents an investigation, which has its main objective in the verification of outdoor wind flow CFD simulation results (ANSYS® Fluent) with real environment measurements in urban setting. The details of the simulation set-up are discussed in the paper including the inlet boundary conditions, surface roughness parameters and the source/sink terms to represent the effect of trees. The simulation results are compared with the high-resolution on-site wind velocity measurements from the Measurement of Turbulence in an Urban Setup (MoTUS) project of Ecole Polytechnique Federale de Lausanne (EPFL) in Switzerland. Multiple simulations were conducted to evaluate the performance of the model based on different wind direction and speeds. At the end of the current study, the highly consistent and accurate results were observed from all 18 verification cases; with the RMSEs of the simulated wind velocities in range of 0.21 and 0.59 m/s only.

Temperature Distributions of the Lumbar Intervertebral Disc during Laser Annuloplasty : A Cadaveric Study

Lee, Min Hyung,Kim, Il Sup,Hong, Jae Taek,Sung, Jae Hoon,Lee, Sang Won,Kim, Daniel H. The Korean Neurosurgical Society 2016 Journal of Korean neurosurgical society Vol.59 No.6

Objective : Low back pain, caused intervertebral disc degeneration has been treated by thermal annuloplasty procedure, which is a non-surgical treatement. The theoretical backgrounds of the annuloplasty are thermal destruct of nociceptor and denaturization of collagen fiber to induce contraction, to shrink annulus and thus enhancing stability. This study is about temperature and its distribution during thermal annuloplasty using 1414 nm Nd : YAG laser. Methods : Thermal annuloplasty was performed on fresh human cadaveric lumbar spine with 20 intact intervertebral discs in a $37^{\circ}C$ circulating water bath using newly developed 1414 nm Nd : YAG laser. Five thermocouples were attached to different locations on the disc, and at the same time, temperature during annuloplasty was measured and analyzed. Results : Thermal probe's temperature was higher in locations closer to laser fiber tip and on lateral locations, rather than the in depth locations. In accordance with the laser fiber tip and the depth, temperatures above $45.0^{\circ}C$ was measured in 3.0 mm depth which trigger nociceptive ablation in 16 levels (80%), in accordance with the laser fiber end tip and laterality, every measurement had above $45.0^{\circ}C$, and also was measured temperature over $60.0^{\circ}C$, which can trigger collagen denaturation at 16 levels (80%). Conclusion : When thermal annuloplasty is needed in a selective lesion, annuloplasty using a 1414 nm Nd : YAG laser can be one of the treatment options.

Biomechanical Study of Lumbar Spinal Arthroplasty with a Semi-Constrained Artificial Disc (Activ L) in the Human Cadaveric Spine

Ha, Sung-Kon,Kim, Se-Hoon,Kim, Daniel H.,Park, Jung-Yul,Lim, Dong-Jun,Lee, Sang-Kook The Korean Neurosurgical Society 2009 Journal of Korean neurosurgical society Vol.45 No.3

Objective : The goal of this study was to evaluate the biomechanical features of human cadaveric spines implanted with the Activ L prosthesis. Methods : Five cadaveric human lumbosacral spines (L2-S2) were tested for different motion modes, i.e. extension and flexion, right and left lateral bending and rotation. Baseline measurements of the range of motion (ROM), disc pressure (DP), and facet strain (FS) were performed in six modes of motion by applying loads up to 8 Nm, with a loading rate of 0.3 Nm/second. A constant 400 N axial follower preload was applied throughout the loading. After the Activ L was implanted at the L4-L5 disc space, measurements were repeated in the same manner. Results : The Activ L arthroplasty showed statistically significant decrease of ROM during rotation, increase of ROM during flexion and lateral bending at the operative segment and increase of ROM at the inferior segment during flexion. The DP of the superior disc of the operative site was comparable to those of intact spine and the DP of the inferior disc decreased in all motion modes, but these were not statistically significant. For FS, statistically significant decrease was detected at the operative facet during flexion and at the inferior facet during rotation. Conclusion : In vitro physiologic preload setting, the Activ L arthroplasty showed less restoration of ROM at the operative and adjacent levels as compared with intact spine. However, results of this study revealed that there are several possible theoretical useful results to reduce the incidence of adjacent segment disease.

Evaluation of Industry 4.0 Data formats for Digital Twin of Optical Components

Arno Schmetz,Tae Hun Lee,Maximilian Hoeren,Marvin Berger,Susanne Ehret,Daniel Zontar,Soo-Hong Min,Sung-Hoon Ahn,Christian Brecher 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.7 No.3

A wide range of software and hardware components are present in today’s production systems and plants using a variety of interfaces and data formats for information exchange on diff erent levels of the system. To increase the traceability, the lifecycle management and providing a single point of source of component-specifi c data, the Digital Twin technology is proposed, linking diff erent data sets tailored to the requirements of diff erent kind of users (e.g., machines, technicians, logistics, manufacturing execution systems). The data exchange between entities in the manufacturing network relies on machine-readable, fl exible and self-describing data formats. When implementing or integrating diff erent components into complex systems, the interoperability challenge is a major concern to address by the system designers and becomes a central task for the creation and integration of Digital Twin technology. In this paper, we evaluate diff erent formats that are used in real environments and create a requirements framework for an ideal format for exchanging fl exible and self-describing data in context of optical components manufacturing process and their special requirements.

Simulation of electrical conductivity for nanoparticles and nanotubes composite sensor according to geometrical properties of nanomaterials

Min, Soo-Hong,Lee, Tae Hun,Lee, Sangwook,Song, Ji-Hyeon,Lee, Gil-Yong,Zontar, Daniel,Brecher, Christian,Ahn, Sung-Hoon Elsevier 2019 Composites Part B, Engineering Vol.174 No.-

<P><B>Abstract</B></P> <P>The nanocomposite based on conductive nanoparticles and nanotubes are widely used for stretchable strain sensors application. Since electrical properties varies by the geometrical properties of nanomaterials, it is important to understand the effects of nanomaterials by strain to optimise the sensor performance. However, it is difficult to fabricate strain sensor using nanomaterials with exactly desired properties. Hence, in this study, we have developed a simulation method for conductive nanoparticles and nanotubes composite using Lennard-Jones potential model and the voter model. First, we optimised the distribution of nanocomposites using Lennard-Jones potential model in the boundary conditions according to external strain. Then, we counted the average attachment among nanomaterials by strain using the voter model which is directly influence electrical conductivity of strain sensors. Moreover, we validated proposed simulation method using experimental value of fabricated strain sensor with various nanocomposite composition ratio and packing ratio. Using the suggested method, the effect of geometrical properties of nanomaterials can be accurately estimated with low simulation cost. Finally, we obtained the simulation value for strain sensor performance by various diameter of nanoparticle, diameter of nanotube, and length of nanotube. We demonstrated that the diameter of nanoparticle is a primary factor for sensor performance while the diameter of nanotubes does not have great influence. Based on the simulation results, it was confirmed that the change of electrical conductivity according to the strain is the largest at small and uniform nanomaterials. The developed simulation method can be applied to the general analysis of electrical properties for nanocomposites.</P>

Controlled crack propagation for atomic precision handling of wafer-scale two-dimensional materials

Shim, Jaewoo,Bae, Sang-Hoon,Kong, Wei,Lee, Doyoon,Qiao, Kuan,Nezich, Daniel,Park, Yong Ju,Zhao, Ruike,Sundaram, Suresh,Li, Xin,Yeon, Hanwool,Choi, Chanyeol,Kum, Hyun,Yue, Ruoyu,Zhou, Guanyu,Ou, Yunbo American Association for the Advancement of Scienc 2018 Science Vol.362 No.6415

<P><B>Cleaving with a metal handle</B></P><P>Using adhesive tape to pull off monolayers of two-dimensional (2D) materials is now a well-established approach. However, the flakes tend to be micrometer scale, and the creation of multilayer stacks for device application can be challenging and time consuming. Shim <I>et al.</I> show that monolayers of a variety of 2D materials, including molybdenum disulfide and hexagonal boron nitride, can be cleaved from multilayers grown as 5-centimeter-diameter wafers. The multilayer is capped with a nickel layer, which can be used to pull off the entire grown stack. The bottom of the stack is again capped with nickel, and a second round of cleaving leaves the monolayer on the bottom nickel layer. The monolayers could be transferred to other surfaces, which allowed the authors to make field-effect transistors with high charge-carrier mobilities.</P><P><I>Science</I>, this issue p. 665</P><P>Although flakes of two-dimensional (2D) heterostructures at the micrometer scale can be formed with adhesive-tape exfoliation methods, isolation of 2D flakes into monolayers is extremely time consuming because it is a trial-and-error process. Controlling the number of 2D layers through direct growth also presents difficulty because of the high nucleation barrier on 2D materials. We demonstrate a layer-resolved 2D material splitting technique that permits high-throughput production of multiple monolayers of wafer-scale (5-centimeter diameter) 2D materials by splitting single stacks of thick 2D materials grown on a single wafer. Wafer-scale uniformity of hexagonal boron nitride, tungsten disulfide, tungsten diselenide, molybdenum disulfide, and molybdenum diselenide monolayers was verified by photoluminescence response and by substantial retention of electronic conductivity. We fabricated wafer-scale van der Waals heterostructures, including field-effect transistors, with single-atom thickness resolution.</P>

Numerical form-finding of multi-order tensegrity structures by grouping elements

Xinyu Wang,Jianguo Cai,Daniel Sang-hoon Lee,Yixiang Xu,Jian Feng 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.41 No.2

Multi-order tensegrity structures are an attractive form of compliant deployable structures. An efficient numerical form-finding method is proposed for multi-stable tensegrity structures in this paper. The current method first analyze the force density matrix for sets of more feasible force densities that satisfy the non-degeneracy conditions. Then, based on symmetrical grouping of elements, a genetic algorithm is used to minimize the eigenvalues; as a result, multiple orders of equilibrium can be found. For the investigation, two symmetric tensegrity structures are analyzed using the currently proposed method, and the method’s applicability and accuracy have been examined.

Structural evaluation of a foldable cable-strut structure for kinematic roofs

Jianguo Cai,Qian Zhang,Yiqun Zhang,Daniel Sang-hoon Lee,Jianfeng Zhao 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.29 No.5

The rapidly decreasing natural resources and the global variation of the climate push us to find intelligent and efficient structural systems to provide more people with fewer resources. This paper proposed a kinematic cable-strut system to realize sustainable structures in responding to changing environmental conditions. At first, the concept of the kinematic system based on crystal-cell pyramid (CP) cable-strut unit was given. Then the deployment of the structure was studied experimentally. After that, the static behaviors in the fully deployed state under the symmetric and asymmetric load cases were investigated. Moreover, the effects of thermal loading and the initial prestress distribution were also discussed. Comparative studies between the proposed structure and other deployable cable-strut system under three times of design load cases were carried out. Finally, the robustness of the system was studied by removal of one passive cable at one time.

Appropriate Smart Factory for SMEs: Concept, Application and Perspective

정우균,Dong-Ryul Kim,Hyunsu Lee,Tae Hun Lee,Insoon Yang,Byeng D. Youn,Daniel Zontar,Matthias Brockmann,Christian Brecher,Sung-Hoon Ahn 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.22 No.1

In the manufacturing industry, the smart factory is considered the final stage of the Fourth Industrial Revolution. Manufacturing companies are pursuing breakthroughs by introducing various advanced technologies to ensure their competitiveness. However, it is difficult for small and medium-sized enterprises (SMEs) to adopt smart-factory technologies, owing to financial and technical burdens. This paper proposes a smart factory that can be applied technically and strategically to the introduction of a smart factory for SMEs. The concept of an ‘appropriate smart factory’ involves applying appropriate measures in terms of cost and scale with consideration of the situations faced by SMEs. The goal is to build a smart factory that has necessary functions (Essential) but can be easily operated (Simple) at a low cost (Affordable) and has compatibility (Interoperable). This paper presents technical application measures such as appropriate smart sensors, appropriate IoT (Internet of Things), and small data processing, along with the definition of an appropriate smart factory. In addition, a case study was examined where the quality inspection equipment for garment manufacturing SMEs was developed by applying the appropriate smart factory concept.