• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.5
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• pp.740-745
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• 1987

For the prediction of the crack growth initiation from a blunt notch or a precrack in a prestrained material under plane strain tension and small-scale yielding conditions, a microscopic fracture criterion is proposed in terms of the crack tip opening displacement(COD) needed for the attainment of fracture strain at a microstructural distance. Smooth blunting of a crack tip with an initial root radius is assumed, and strain distributions on the crack-line axis are calculated at each deformation stage until the distributions against an original distance normalized to the COD are insensitive to an initial root radius. This case of no initial-root-radius effect is taken as for a sharp crack tip, on which the criterion is applied to determine the characteristic length of material from a critical COD for a fatigue-precracked specimen. The predicted COD at the fracture initiation from a crack with an initial root radius or a prestraining shows reasonable agreement with experimental values.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.7
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• pp.3393-3412
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• 2017

As a main challenge in network virtualization, virtual network embedding problem is increasingly important and heuristic algorithms are of great interest. Aiming at the problems of poor correlation in node embedding and link embedding, long distance between adjacent virtual nodes and imbalance resource consumption of network components during embedding, we herein propose a two-stage virtual network embedding algorithm NA-PVNM. In node embedding stage, resource requirement and breadth first search algorithm are introduced to sort virtual nodes, and a node fitness function is developed to find the best substrate node. In link embedding stage, a path fitness function is developed to find the best path in which available bandwidth, CPU and path length are considered. Simulation results showed that the proposed algorithm could shorten link embedding distance, increase the acceptance ratio and revenue to cost ratio compared to previously reported algorithms. We also analyzed the impact of position constraint and substrate network attribute on algorithm performance, as well as the utilization of the substrate network resources during embedding via simulation. The results showed that, under the constraint of substrate resource distribution and virtual network requests, the critical factor of improving success ratio is to reduce resource consumption during embedding.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.7
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• pp.548-554
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• 2003

This study alms to investigate the dynamic properties of express buses in the very low frequencies which cause motion sickness Incidence. Since passengers often use express buses for long distance traveling. it is a critical point whether the ride give rise to motion sickness or not. In the study accelerations at the three Points on the floor of the six test vehicles were measured during the driving at constant speeds. By applying the frequency weighting corves suggested in ISO 26.31-1, the Physical quantity of accelerations were changed into the perceptual amount used to judge quantitatively the incidence of motion sickness. Motion sickness dose values were calculated from the frequency weighted time history of acceleration signals, and compared between the vehicles, driving conditions. and the seat positions in the bus. During the 50 minutes' driving on the public road and high ways. the vomiting incidence ratios were seen to range from 0.4 to 0.8 ％. which is equivalent to 2.4 to 4.8 ％ for 5 hours' driving. Unlike the very smooth road conditions considered in this work, motion sickness dose values encountered in real situations are expected to increase.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.5 no.3
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• pp.117-126
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• 1985

The object of this study is experimental determination of the refraction coefficient(K) which is critical factor in the zenith distance measurement of precision trigonometrical leveling. Thus, the characteristics of seasonal, directional and daily variation of the refraction coefficients according to each district were presented in this paper. Comparing K value by the observed zenith distance with that calculated from the temperature gradient observed at Mt. Mudeung, we obtained satisfactory results.

• Progress in Superconductivity
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• v.8 no.1
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• pp.8-15
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• 2006

The size of the superconducting domains and the critical current density inside these domains have to be enhanced for most of cryomagnetic applications of melt-textured YBCO bulks. To enlarge the size of the domains we studied the multi-seeding technique based on a well-established procedure for preparing high quality YBCO monoliths using self-made SmBCO seeds. The distance between the seeds was optimised as a result of the investigation of the effects of various seed distances on the characteristics of the grain boundary Junctions. The influences of a-b plane intersections and c-axis misalignments were researched. Thereby, a small range of tolerance of the misorientations between the seed crystals was found. Field mapping was applied to control the materials quality and the superconductor's grain structure was investigated using polarisation microscopy. YBCO function elements with iou. seeds in a line and an arrangement of making type (100)/(100) and (110)/(110) boundary junctions, respectively, were processed. The trapped field profile in both sample types shows single domain behaviour. To demonstrate the potential of the multi-seeding method a ring-shaped sample was processed by placing sixteen seeds in a way to make both (100)/(100) and (110)/(110) grain junctions at the same time. The results up to now are very promising to prepare large single domain melt-textured YBCO semi-finished products in complex shapes.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.23 no.6
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• pp.533-538
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• 2014

We fabricated grooved mushroom structures with anisotropic wettability on silicon substrates using basic MEMS processes. The geometry of these grooved mushroom structures could be changed by controlling the additional IPA solution during Si etching by TMAH solution. To understand anisotropic wettability, contact angles (CAs) of hexadecane droplets were measured in the orthogonal and parallel directions to grooved lines. The CA measurement results displayed anisotropic wetting on the grooved mushroom structures. However, specimens with $80{\mu}m$ distance between top layers displayed isotropic and superoleophobic wetting. This study demonstrates that the thickness of the top layer is more critical than the width or height of the ridge when determining the wettability of organic solvent. Despite the wide distance between top layers ($80{\mu}m$), the specimen with a thin top layer (100 nm) showed highly anisotropic wetting and low CA due to the pinning of droplets at the edge of the top layer.

• Journal of Welding and Joining
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• v.24 no.1
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• pp.88-92
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• 2006

Laser-rotating arc hybrid welding was introduced by combining $CO_2$ laser and rotating gas metal arc welding. While the arc rotation enhances the weld pool motion, it reduces the undercut formation which is one of most critical weld defects in the conventional laser-arc hybrid welding. This research investigated the bead characteristics according to the welding parameters such as frequency of rotation, welding voltage, shielding gas composition and interspacing distance between laser and we. The welding parameters were selected to reduce spatter generation and ensure sound weld beads fur bead welding and butt welding with various joint gaps. Gap bridging ability was improved, such that the sound weld beads were achieved for butt joint with up to 2mm joint sap, with no adjustment of CTWD(Contact tip-to-workpiece distance) and electrode diameter.

• Transactions of the Society of Information Storage Systems
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• v.3 no.1
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• pp.1-4
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• 2007

A high density optical data storage device has been required for many years. In the field of the optical data storage, a near-field recording (NFR) technology is considered as a next generation one for achieving the high data density. Due to an evanescent wave effect occurred under 100nm distance which is the excessively small distance between the SIL and the disc, the most significant and difficult problem in this technology is to maintain a gap between a solid immersion lens (SIL) and a disc. Also, maintaining the gap under at least 50nm is required in the NFR gap servo system to use the evanescent wave effect efficiently. There are some institutes that have shown the novel gap servo control. In general, they use a mode switching servo method which consists of approach, hand-over and gap control mode. However there is a critical problem such as an overshoot at the tuning point from the approach mode to the hand-over mode, which may cause a collision between the SIL and the disc. In this paper, we show our NFR system and an improved gap servo system using an exponential function as the approach mode which can reduce the overshoot.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.234-240
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• 2003

This study aims to investigate dynamic properties of express buses in the very low frequencies which affect motion sickness incidence. Since passengers often use express buses for long distance traveling, it is a critical point whether a give rise to motion sickness or not. In the study accelerations at the three points on the floor of the six test vehicles were measured during the driving at constant speeds. By applying frequency weighting curves suggested in ISO 2631-1 and ISO 2631-3, physical amount of accelerations were changed into perceptual amount which determines incidence of motion sickness. Motion sickness dose values were calculated from the frequency weighted time history of accelerations, and compared between the vehicles, driving conditions, and the seat positions in the bus. During the driving on public road and high ways for 50 minutes vomiting incidence ratios ranged 0.4 to 0.8%, which were equivalent to 2.4 to 4.8% for 5 hours' driving. The value of 4.8 % means two among 45 passengers may vomit after the traveling, which is very serious situation. Considering the very smooth driving condition at which the data were collected, motion sickness dose values will increase in real situations

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.12
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• pp.620-625
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• 2015

The summer climate is very hot and humid in Korea. Humidity is an important factor in determining thermal comfort. Recently, research on dehumidification device development has been attempted to save the energy required for operating the dehumidifier. Existing dehumidification systems have disadvantages such as wasting energy to drive the compressor. Meanwhile, dehumidification systems with membranes can dehumidify humid air without increasing the dry bulb temperature. Therefore. they don't have to consume cooling energy. In this paper, the installation conditions for a membrane system were analyzed to improve the shape and optimum performance of the system. The results showed that the distance between elements was the critical system design factor, and that a distance of 20 mm was the optimal condition for the pressure drop and flow characteristics of the internal air flow.