• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.15.1-15.1
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• 2009

Nano transfer printing and micro contact printing is well known printing method based on soft lithography which uses conformal soft elastomer with designed surface relief structures. Here I introduce another class of novel 3D nanofabrication technique by using the same elastomer but in a different manner. The approach, which we refer to as proximity field nanopatterning, uses the surface-reliefed elastomers as phase masks to pattern thick layers of transparent, photosensitive materials. Aspects of the optics, the materials, and the physical chemistry associated with this method are outlined. A range of 3D structures illustrate its capabilities, and several application examples demonstrate possible areas of use in technologies ranging from microfluidics to photonic materials to density gradient structures for chemical release and high-energy density science.

• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.3
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• pp.180-191
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• 2022

In this paper, a single-stage alternating current (AC)-DC converter is proposed for the automated-guided vehicle wireless charging system. The proposed converter is capable of soft-switching under all input voltage (VAC: 220 Vrms ± 10%), load conditions (0-1 kW), and air gap changes (40-60 mm) by phase control at a fixed switching frequency. In addition, controlling a wide output voltage (Vo: 39~54 VDC) is possible by varying the link voltage and improving the input power factor and the total harmonic distortion factor. Experimental results were verified by making a prototype of a 1-kW wireless power charging system that operates with robustness to changes in air gaps.

• Transactions of Materials Processing
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• v.15 no.6 s.87
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• pp.436-440
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• 2006

A rapid tooling (RT) method fur the resin transfer molding (RTM) have been investigated. We fabricated a curved I-beam to verify the method. After creating a three-dimensional CAD model of the beam we fabricated a prototype of the model using a rapid prototyping (RP) machine. A soft mold was made using the prototype by the conventional silicone mold technique. The procedure and method of mold fabrication is described. The mold was cut into several parts to allow easier placement of the fiber preform. We conducted the resin transfer molding process and manufactured a composite beam with the mold. The preform was built by stacking up eight layers of delicately cut carbon fabrics. The fabrics were properly stitched to maintain the shape while placement. The manufactured composites beam was inspected and found well-impregnated. The fiber volume ratio of the fabricated beam was 16.85%.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.33B no.10
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• pp.148-156
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• 1996

Increasing the switching frquency is essential to achieve the high density of switched mode power supplies, but this leads to the increase of switching losses. A number of new soft switching converters have been presented ot reduce switching losses, but most of them may have some demerits, such as the increase of voltage/current stresses and high conduction losses. To overcome these problems, the ZVT-PWM converter has recently been presented. in this paper, the operation characteristics of the ZVT-PWM boost converter is analyzed, and the steady-states (DC) and small-signal model of this converter are derived and analyzed, and then the transfer functions of this converter are derived. The transfer functions of ZVT-PWM boost converter are similar to those of the conventional PWM boost converter, but the transfer characteristics are affecsted by te duty ratio and the switching frequency.

• Archives of Reconstructive Microsurgery
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• v.10 no.2
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• pp.154-162
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• 2001

Diabetic foot ulcer is a serious complication which result from long-standing diabetes. Especially, severe infected diabetic foot ulcer results in unwanted lower extremity amputation. The diabetic patient is considered the relative contraindication for microsurgery because of the severe peripheral vascular disease. Recently, microvascular free tissue transfer technique applied to diabetic foot ulcer. It is well known that free tissue transfer provides immediate soft tissue coverage and control of infection. So it is possible that preservation of the lower extremity through free tissue transfer. A retrospective study of diabetic patients who had infected foot ulcer from 1999 to 2000 with foot defects reconstructed with free tissue transfer were reviewed. Thirteen patients were studied with mean follow-up of 12.7 months. There were two deaths during follow-up period. There were two failures after free flap surgery. All eleven survived patients were ambulatory. There was no recurrence of ulcer. No patient need amputation above the ankle joint. We have found that free tissue transfer for infected diabetic foot ulcer is very effective surgical technique. Careful patient selection and regular follow-up is important.

• Archives of Reconstructive Microsurgery
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• v.10 no.2
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• pp.75-80
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• 2001

Purpose : We have evaluated the morbidity of donor site after transfer of free fibular osseous and osteocutaneous flap to defect site of bone and soft tissue due to chronic osteomyelitis of long tubular bone, open fracture with bony defect, bone or soft tissue tumor and congenital anomaly. Materials and methods : The 54 cases of 79 cases to be carried out from May, 1982 to May, 2001 which could be followed up were reviewed. There were forty nine in male and five in female. The mean age was 35(4 to 66)years old and mean follow up period is 21.3 month(12 to 72). We have retrospectively analyzed the various postoperative complications such as compartment syndrome, donor site infection, skin defect, hypesthesia, hammer toes, ankle instability and activity of daily living by help of questionnaire, telephone, physical examination, follow up x-ray study and chart. Results : In the total 54 cases the medication period for pain control after operation were classified into three groups under 2 weeks(49 cases), from 2 weeks to 6 weeks(3 cases) and over 6 weeks(2 cases). The postoperative morbidity were occurred in total 12 cases(compartment syndrome: 0, infection : 2, skin defect: 1, hypesthesia: 5, hammer toe: 2 ankle pain: 2 discomfort in activity of daily living: 0), and also the morbidity rates of donor site were 23.5% in osseous flap and 21.6% in osteocutaneous flap were occurred. There was no statistical significonce in morbidity between osseous and osteocutaneous free fibular flap transfer(P>0.05). Discussion : In general the morbidity of free fibular flap transfer was relatively high but it did not have any effect on daily activity of living. We think that the meticulous operation technique, detailed wound care and early range of motion exercise will reduce the morbidity of donor site of flap.

• Journal of the Korean Geosynthetics Society
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• v.9 no.3
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• pp.9-18
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• 2010

A series of model tests were performed to investigate the load transfer by soil arching in geosynthetic-reinforced and pile-supported(GRPS) embankment systems. In the model tests, model piles with isolated cap were inserted in the model container and geosynthetics was laid on the pile caps below sand fills. The settlement of soft ground was simulated by rubber form. The loads acting on pile caps and the tensile strain of geosynthetics were monitored by data logging system. At the given interval ratio of pile caps, the efficiency in GRPS embankment systems increased with increasing the height of embankment fills, then gradually converged at constant value. Also, at the given height of embankment fills, the efficiency decreased with increasing the pile spacing. The embankment loads transferred on pile cap by soil arching increased when the geosynthetics installed with piles. This illustrated that reinforcing with the geosynthetics have a good effect to restraint the movement of surrounding soft grounds. The load transfer in GRPS embankment systems was affected by the interval ratio, height of fills, properties of grounds and tensile stiffness and so on.

• Journal of the Korean Society for Railway
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• v.12 no.2
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• pp.276-284
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• 2009

Recently pile-supported embankments have emerged as an optimum method when the rapid construction and strict deformation of structures are required on soft soils. Especially geosynthetic-reinforced and pile-supported (GRPS) embankments are used worldwide as they can provide economic and effective solutions. However the load transfer mechanism in GRPS embankments is very complex, and not yet fully understood. Particularly the purpose and effect of geosynthetic inclusion are ambiguous and considered as an auxiliary measure assisting the arching effect of piles. Numerical parametric study using 3D finite element method has been conducted to investigate the effect of geosynthetic reinforcement on the load transfer mechanism of GRPS embankments. Numerical results suggested that as more stiffer geosynthetic is included, arching effect decreases considerably and the load concentration to the piles mostly caused by tension effect of geosynthetic. This finding is contradictory to the common understanding that geosynthetic inclusion only enhance the efficiency of load transfer. Consequently the design parameters determined from the numerical analyses are compared with those of three existing design methods. The problems of the existing methods are discussed.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.49-56
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• 2005

The negative skin friction on piles, which are installed in currently consolidating soft deposits, creates significant problems on the stability of pile foundations. This study investigated whether or not the pile foundation designs were appropriate in soft deposits with large amount of consolidation settlement. The final settlements of the grounds along the pile depth were estimated by the soil parameters obtained from the laboratory tests and by the field-measured settlement curves, if they were available. The displacement of the piles along the pile depth was estimated by both the load transfer method and the numerical method. Both methods gave similar locations of neutral points and magnitudes of the maximum axial forces. The movements of the ground and the piles were compared to calculate the down drag acting on piles. For the piles whose bearing capacities were less than the design loads including the down drag, slip layer coatings and/or incrementing of the penetration depth into the bearing stratum were proposed to improve the piles capacities.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.1695-1704
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• 2008

The problems associated with constructing high-speed concrete track embankments over soft compressible soil has lead to the development and/or extensive use of many of the ground improvement techniques used today. Drains, surcharge loading, and geosynthetic reinforcement, have all been used to solve the settlement and embankment stability issues associated with construction on soft soils. However, when time constraints are critical to the success of the project, owners have resorted to another innovative approach. Especially, the design criteria of residual settlement is limited as 30mm for concrete track embankment, it is very difficult to satisfy this standard using the former construction method. Pile net method consist of vertical columns that are designed to transfer the load of the embankment through the soft compressible soil layer to a firm foundation and one or more layers of geosynthetic reinforcement placed between the top of the columns and the bottom of the embankment. This paper will present the guidelines for the design of pile net method to supported embankments. These guidelines were developed based on a review of current design methodologies and a parametric study of design variables using numerical modeling.