• Structural Engineering and Mechanics
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• v.86 no.4
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• pp.519-533
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• 2023

This work focuses on the dynamic analysis of thermal barrier coated straight and curved turbine blades modelled as functionally graded sandwich panel under thermal environment. The pre- twisted straight/curved blade model is considered to be fixed to the hub and, the complete assembly of the hub and blade are assumed to be rotating. The functionally graded sandwich composite blade is comprised of functionally graded face-sheet material and metal alloy core. The constituents' material properties are assumed to be temperature-dependent, however, the overall properties are evaluated using Voigt's micromechanical scheme in conjunction with the modified power-law functions. The blade model kinematics is based on the equivalent single-layer shear deformation theory. The equations of motion are derived using the extended Hamilton's principle by including the effect of centrifugal forces, and further solved via 2D- isoparametric finite element approximations. The mesh refinement and validation tests are performed to illustrate the stability and accurateness of the present model. In addition, frequency characteristics of the pre-twisted rotating sandwich blades are computed under thermal environment at various sets of parametric conditions such as twist angles, thickness ratios, aspect ratios, layer thickness ratios, volume fractions, rotational velocity and blade curvatures which can be further useful for designing the blade type structures under turbine operating conditions.

• International Journal of Railway
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• v.1 no.4
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• pp.149-156
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• 2008

During maintenance or construction works in or at the tracks of railways, high risks for passengers and railway staff, especially for the workers on the construction site exist. The high risks result out of the movement of rail vehicles, like trains or construction vehicles, which must be faced by using any available technical and operational technologies for securing them against the environment. Therefore, it is necessary to evaluate the level of protection continuously and to identify new and innovative methods and technologies for the protection of the gang (construction worker, machines and material). Especially on construction sites at line sections with two or more parallel tracks but also with single tracks, there are still a lot of incidents and accidents mostly with seriously injured persons or fatalities. These were mainly gang members that breach the railway-loading gage. By using proper warning or protection systems, the avoidance of such accidents must be achieved. The latest developments. in gang protection systems concern on the one hand fixed barriers in the middle between the construction site and the operated track and on the other hand construction vehicles equipped with automatic warning systems. The disadvantage of such protection methods is that the gang can be warned against an approaching train but a monitoring of the gang members cannot be performed. Only one part of a potential dangerous situation will be detected. If the gang members will overhear the acoustic warning signal of the security staff and the workers will not leave the danger zone in the track, the driver of the approaching train had no chance to react to the dangerous situation. An accident is often inevitable. While the detection of acoustic warning signals by the gang members working on a construction site is very difficult, the acoustical planning of an automatic warning system has to be designed for an acoustic short range level of one meter besides the construction vehicle. The decision about the use of today's technical warning system (fixed systems, automatic warning systems, etc.) must be geared to the technical feasibility and the level of safety which is needed. Criteria for decision guidance to block a track should be developed by danger estimation and economical variables. To realize the actual jurisdiction and to minimize the hazards of railway operations by the use of construction vehicles near the tracks further developments are needed. This means, that the warning systems have to be enhanced to systems for protection, which monitor the realization of the warning signal as a precondition for giving a movement authority to a train. This method can protect against accidents caused by predictable wrongdoing. The actual state of the art technique of using a collective warning combined with additional security staff is no longer acceptable. Therefore, the Institute of Transportation System of the German Aerospace Center in Braunschweig (Germany) will develop a gang warning and protection system based upon imaging methods, with optical sensors such as video in visible and invisible ranges, radar, laser, and other. The advantage of such a system based on the possibility to monitor both the gang itself and the railway-loading gauge either of the parallel track or of the same track still in use. By monitoring both situations, the system will be able to generate a warning message for the approaching train, that there are obstacles in the track, so that the train can be stopped to prevent an accident. And also the gang workers will be warned, while they breach their area.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.6
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• pp.549-558
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• 2012

A topology optimization method for phononic crystals is developed for the design of sound barriers, using the level set approach. Given a frequency and an incident wave to the phononic crystals, an optimal shape of periodic inclusions is found by minimizing the norm of transmittance. In a sound field including scattering bodies, an acoustic wave can be refracted on the obstacle boundaries, which enables to control acoustic performance by taking the shape of inclusions as the design variables. In this research, we consider a layered structure which is composed of inclusions arranged periodically in horizontal direction while finite inclusions are distributed in vertical direction. Due to the periodicity of inclusions, a unit cell can be considered to analyze the wave propagation together with proper boundary conditions which are imposed on the left and right edges of the unit cell using the Bloch theorem. The boundary conditions for the lower and the upper boundaries of unit cell are described by impedance matrices, which represent the transmission of waves between the layered structure and the semi-infinite external media. A level set method is employed to describe the topology and the shape of inclusions. In the level set method, the initial domain is kept fixed and its boundary is represented by an implicit moving boundary embedded in the level set function, which facilitates to handle complicated topological shape changes. Through several numerical examples, the applicability of the proposed method is demonstrated.

• Journal of Periodontal and Implant Science
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• v.35 no.4
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• pp.939-948
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• 2005

The role of the periosteum on osteointegration of $Bio-Oss^{(R)}$(Geistlich, Wolhusen/Switzerland) was studied in rabbit calvarial defect. 12 New Zealand white male rabbits between 2.8 and 4 kg were included in this randomized, blinded, prospective study. Each rabbit was anesthetized with Ketamine HCl(5 mg/kg) and Xylazine HCl(1.5 ml/kg). An incision was made to the bony cranium and the periosteum was reflected. Using a 6-mm trephine bur(3i. USA), four 8-mm defects were created with copious irrigation. The defects were classified into barrier membrane($Tefgen^{(R)}$, Lifecore Biomedical. Inc, U.S.A.) only group as a control, $Bio-Oss^{(R)}$ with barrier membrane group, $Bio-Oss^{(R)}$ with periosteum covering group, and $Bio-Oss^{(R)}$ without periosteum covering group. There were 2 rabbits in each group. The wound was closed with resorbable suture materials. Rabbits were sacrificed using phentobarbital(100 mg/kg) intravenously at 1, 2, and 4 weeks after surgery. The samples were fixed in 4% paraformaldehyde, and decalcified in hydrochloric acid decalcifying solution(Fisher Scientific, Tustin, CA) at $4^{\circ}C$ for 2-4 weeks. It was embedded in paraffin and cut into 6 ${\mu}m$ thickness. The sections were stained with H & E and observed by optical microscope. The results were as follows; 1. The periosteum played an important role in osteointegration of $Bio-Oss^{(R)}$ in bone defects. 2. When the periosteum remained intact and $Bio-Oss^{(R)}$ was placed on the defect, $Bio-Oss^{(R)}$ with periosteum covering has been incorporated into the newly formed bone from 2-week postoperatively. 3. When the periosteum was removed at the surgical procedure, invasion of connective tissue took place among the granules, and new bone formation was delayed compared to periosteum covering group. Therefore, when the bone grafting was performed with periosteal incision procedure to achieve tension-free suture, the integrity of the overlying periosteum should be maintained to avoid fibrous tissue ingrowth.

• Environmental and Resource Economics Review
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• v.22 no.4
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• pp.785-815
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• 2013

This paper analyzes the three issues related to the effect of environmental regulations on the Korean trades with gravity equation model: the effect on the Korean exports, the bilateral trade flows between the Korea and the trade partners, and the Korean international competitiveness. For all three issues we carried the empirical tests with fixed effect estimation methods for total industries, non-pollution industries, pollution industries, and also 16 individual pollution industries. We use industry panel data for the 120 largest trading countries with Korea for the years 2000-2010. The Environmental Performance Index (EPI) is used as the proxy variable for the environmental regulation. The empirical result shows that while GDPs of both Korea and its trading partners are very important factors affecting positively the Korean trades for all industries, the environmental regulation of the importing country would be a definite trade barrier to the Korean pollution industries, but not a definite one for the non-pollution industries. In addition, the stricter environmental regulations of Korea's trade partners would weaken the Korean international competitiveness of Korean pollution industries. In this regard, the Porter Hypothesis would have not appeared in the Korean trades of pollution industries during the period observed in this study.

• The Journal of Engineering Geology
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• v.23 no.2
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• pp.127-136
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• 2013

We analyzed the patent trends for whole drilling bits to reveal the main R&D directions, focusing on patents applied for and registered in Korea, the USA, Japan, and Europe. The technology was classified into two groups as a primary classification step (reaming systems and fixed systems), and into seven groups as a secondary classification step (sliding, odex, horizontal pivot, vertical pivot, concentric, eccentric, and etc.). A total of 33,614 patents were retrieved and 870 patents were selected for final effective analysis by data deduplication and filtering. A portfolio analysis using the correlation between the number of patents and the applicants for each patents revealed a sliding system as the key technology with greatest growth potential. From an analysis of the barriers to patents being granted, we emphasize the need to avoid similar topics existing patents or patent applications and to develop differential technology.

• Journal of the Korean Vacuum Society
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• v.22 no.6
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• pp.335-340
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• 2013

This paper is for the simulation design to enhance the breakdown voltage of MHEMTs with an InP-etchstop layer. Gate-recess and channel structures has been simulated and analyzed for the breakdown of the MHEMT devices. The fully removed recess structure at the drain side of MHEMT shows that the breakdown voltage enhances from 2 V to almost 4 V as the saturation current at gate voltage of 0 V is reduced from 90 mA to 60 mA at drain voltage of 2 V. This is because the electron-captured negatively fixed charges at the drain-side interface between the InAlAs barrier and the $Si_3N_4$ passivation layers deplete the InGaAs channel layer more and thus decreases the electron current passing the channel layer and thus the impact ionization in the channel become smaller. In addition, the replaced InGaAs/InP composite channel with the same thickness in the same asymmetrically recessed structure increases the breakdown voltage to 5 V due to the smaller impact ionization and mobility of the InP layer at high drain voltage.

• Journal of the Korean Institute of Landscape Architecture
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• v.35 no.3
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• pp.1-12
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• 2007

This study aims to examine the existing conditions of elderly housing facilities and to understand the characteristics and types of outdoor living environments utilized by the elderly. To achieve this, this study relied on two methods: a descriptive method of researching publications and related scholastic writings, and an empirical study that included a survey of present conditions and interviews with the elderly and their nursing care providers. Additionally, evaluation of usage patterns and physical traces were carried out in twelve cases. First, the study showed that all of the facilities, which are fixed in particular areas, had difficulty providing spatial diversity that met the needs of residences. This means that these areas lack flexibility. Activity programs were, however, carried out in a lively manner in well-equipped spaces. Second, an evaluation of outdoor living environments showed that basic facilities were more than adequate, in general. Consideration of resident's physical strength and taste, however, was evaluated as low, indicating that facilities and spaces should be considered to reflect the ages, physical capacity, diverse tastes and hobbies of the elderly, as well. Third, examining the usage patterns of outdoor living activities of residents, the purposes of using outdoor spaces of elderly housing facilities were mainly 'to take a walk' and 'to engage in simple physical exercise' and the walkway, simple sports facilities, and building entrances were highly utilized. The importance of outdoor living environments values was a mean of 4.07 and satisfaction was 4.17. This indicates that residents thought that outdoor living environments are very important and currently satisfied with them.

• Journal of the Korea Institute of Military Science and Technology
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• v.12 no.1
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• pp.123-132
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• 2009

Civil petitions and law suits against the military rifle shooting noise have been increased because many military shooting ranges are located near civilian residential area. In order to solve the noise problems, military have devised various methods. In this study, propagation properties of rifle shot through atmosphere were investigated. The military rifle shooting noise level at 5m from muzzle was between $l14{\sim}120dB$ in all directions. The noise level loom both backward and sideward away from system firing range consisting lines of 8 shooting locations were 90dB, when shots were all fired within 10 seconds. At present some of military bases established sound barriers, muzzle enclosures, silencers, and indoor shooting ranges to reduce noises and these prevention methods can reduce noise by $5{\sim}20dB,\;5{\sim}9dB,\;5{\sim}13dB,\;40{\sim}50dB$, respectively. Even though indoor shooting range has the best performance, it requires very expensive construction cost and has short length between target and shooter. In comparison, muzzle enclosure is cheap, but because it is installed in fixed position it can only be used in one shooting position. Therefore a commander should select appropriate methods to reduce military rifle shooting noise considering distance from residential area to the range, mission of military training, budget, etc.

• Journal of Biomedical Engineering Research
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• v.27 no.5
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• pp.224-228
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• 2006

The object of this study is to investigate the potential of dual-electrospun polymer based structure for vascular tissue engineering, especially for the medium or small sue blood vessels. Polyurethane(PU), which is known to be biocompatible in this area, was electrospun with poly(ethylene oxide) (PEO). Concentration of PU was fixed at 20wt%, while that of PEO was set from 15 to 35wt%. Morphological features were observed by SEM image and measurement of porosity and cellular responses were tested before and after extracting PEO from the hybrid scaffolds by immersing the scaffolds into distilled water. The diameter of PEO fibers were ranged from 200nm to 500nm. The lower concentration of PEO tended to show beads. The porosity of the scaffolds after extracting PEO was highly increased with higher concentration of PEO as expected. Also, higher proliferation rate of smooth muscle cells was observed at higher concentration of PEO than at the lower concentration and without PEO. As conclusions, this dual electrospinning technique combined with PU and PEO is expected to overcome the current barrier of cell penetration by providing more space for cells to proliferation.