• Wind and Structures
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• 제23권2호
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• pp.91-107
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• 2016

Flow-excited acoustic resonance in ducted cavities can produce high levels of acoustic pressure that may lead to severe damage. This occurs when the flow instability over the cavity mouth, which is created by the free shear layer separation at the upstream edge, is coupled with one of the acoustic modes in the accommodating enclosure. Acoustic resonance can cause high amplitude fluctuating acoustic loads in and near the cavity. Such acoustic loads could cause damage in sensitive applications such as aircraft weapon bays. Therefore, the suppression and mitigation of these resonances are very important. Much of the work done in the past focused on the fluid-dynamic oscillation mechanism or suppressing the resonance by altering the edge condition at the shear layer separation. However, the effect of the downstream edge has received much less attention. This paper considers the effect of the impingement edge geometry on the acoustic resonance excitation and Strouhal number values of the flow instabilities in a ducted shallow cavity with an aspect ratio of 1.0. Several edges, including chamfered edges with different angles and round edges with different radii, were investigated. In addition, some downstream edges that have never been studied before, such as saw-tooth edges, spanwise cylinders, higher and lower steps, and straight and delta spoilers, are investigated. The experiments are conducted in an open-loop wind tunnel that can generate flows with a Mach number up to 0.45. The study shows that when some edge geometries, such as lower steps, chamfered, round, and saw-tooth edges, are installed downstream, they demonstrate a promising reduction in the acoustic resonance. On the other hand, higher steps and straight spoilers resulted in intensifying the acoustic resonance. In addition, the effect of edge geometry on the Strouhal number is presented.

• Design & Manufacturing
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• 제8권1호
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• pp.40-44
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• 2014

As a rotating machine element, plastic gears are more and more widely used in such as industrial machine element, since plastic gear is lighter, higher wear-resistance, and higher vibration absorbing ability than metal gears. When operating plastic parts, tooth breakage and fatigue life shortened due to increasing number of applying load and tooth flank temperature rising, such that accuracy of plastic gears is divided from allowable range to cause vibration and noise. On this study, a internal plastic gears are developed which improved the filling balance molding process by a new injection mold structure. The new mold structure called HR3P(hot runner type 3plate mold). As the result from this studies, we obtained a very accurate roundness internal gears by using design of experiment.

• 대한치과교정학회지
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• 제6권1호
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• pp.33-38
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• 1976

For the purpose of evaluating the response of the periodontal tissue in relation to the experimental tooth movement, orthodontic force was applied to 15 female rats. The animals were investigated histopathologically and histochemically by several staining methods. Findings were as follows: 1. The application of 60gm on the rat's molar caused mesial tipping movement and undermining resorption. 2. One day after the insertion of the appliance, the osteoblast was increased in activity but not in number. 3. The osteoclastic activity was decreased as soon as removing the appliance. 4. With the P.A.S. staining, osteoclasts Stained mildly in the initial stage and stained more intensely in the last stage. Osteoclasts revealed negative reaction in the initial stage and stained mildly in the last stage. 5. Slides stained with toluidine blue revealed no conclusive variations between osteoblasts and osteoclasts.

• Tribology and Lubricants
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• 제23권4호
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• pp.149-155
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• 2007

The CAD model of a elliptical gear for wire cutting has been developed. The rolling contact of pitch ellipses whose rotation axes coincide with their focus has been analyzed, and the perimeter of the pitch ellipse has been divided into equal-length segments by the number of teeth. A master tooth profile, which is a composite curve of circular arcs that represents involute, has been introduced. The elliptical gear has been designed by imposing the master tooth on the divided points of the pitch ellipse, and a full fillet has been achieved between neighbour teeth. Thus, the whole profile of an elliptical gear is a composite curve of arcs only, and consequently NC codes for wire cutting can be easily generated. Furthermore, a computer simulation program is developed to verify the mesh of the elliptical gear.

• 대한치과의사협회지
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• 제48권1호
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• pp.56-62
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• 2010

In recent years, a number of special treatment procedures have been introduced to reestablish new tooth supporting tissues with varying degrees of success including guided tissue regeneration(GTR), bone grafting(BG) and the use of enamel matrix derivative(EMD). EMD is an extract of enamel matrix and contains amelogenins of various molecular weights. Emdogain(EMD) might have some advantages over other methods of regenerating the tissue supporting teeth lost by gum disease, such as less postoperative complications. Emdogain contains proteins(derived from developing pig teeth) believed to regenerate tooth attachment. The decrease in probing depth after EMD treatment is achieved primarily by clinical attachment gain and bone regeneration and only to a minor extent by gingival recession. In conclsion, EMD seems to be safe, was able to regenerate lost periodontal tissues in previously diseased sites based on clinical parameters.

• 한국금형공학회:학술대회논문집
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• 한국금형공학회 2008년도 하계 학술대회
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• pp.129-133
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• 2008

As a rotating machine element, plastic gears are more and more widely used in such as industrial machine element, since plastic gear is lighter, higher wear-resistance, and higher vibration absorbing ability than metal gears. When operating plastic parts, tooth breakage and fatigue life shortened due to increasing number of applying load and tooth flank temperature rising, such that accuracy of plastic gears is divided from allowable range to cause vibration and noise. On this study, a internal plastic gears are developed which improved the filling balance molding process by a new injection mold structure. The new mold structure called HR3P(hot runner type 3plate mold). As the result from this studies, we obtained a very accurate roundness internal gears by using design of experiment.

• Tribology and Lubricants
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• 제24권5호
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• pp.221-227
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• 2008

This paper presents a step-by-step design of noncircular gears. From the diagram of angular velocity ratio of a noncircular gear pair, the pitch curves of the two mating gears are determined, and the perimeter of the pitch curve has been divided into equal-length segments by the number of teeth. A master tooth profile, which is a composite curve of circular arcs that represents involute, has been introduced. A noncircular gear pair has been designed by imposing the master tooth on the divided points of the pitch curve, and a full fillet has been achieved between neighbour teeth. Thus, the whole profile of the noncircular gear is a composite curve of arcs only, and consequently NC codes for wire EDM can be easily generated.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제47권1호
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• pp.57-61
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• 2021

Immediate implant placement (IIP) in fresh extraction sockets exhibits similar survival and success rates to delayed implant placement in healed sockets. Several advantages of IIP involve shortened total treatment time, reduction of the number of invasive surgeries, and subsequent reduction of patient discomfort due to lack of additional surgeries. The major shortcomings in IIP, however, include the inability to obtain early bony support, presence of a gap between the extraction socket and fixture, and the inability to cover the fixture with soft tissue, leading to increased risk of infection and implant loss. When IIP is performed, atraumatic or minimally traumatic extractions, conservation of the septal bone in molars, minimal flap elevation or flapless surgery, bone grafting the gap between the fixture and the extraction socket, and coverage with soft tissue or a membrane must be considered.

• Journal of Periodontal and Implant Science
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• 제37권3호
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• pp.637-646
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• 2007

Implants placed immediately after tooth extraction have been shown to be a successfully predictable treatment modality. Several clinical papers suggest that placing implants immediately after tooth extraction may provide some advantages: reduction of the number of surgical procedures or patient visits, preservation of the dimensions of alveolar ridge, and shortening of the interval between the removal of the tooth and the insertion of the implant supported restoration. In this case report, three patients received single immediate implant placements to replace a maxillary anterior tooth at the time of extraction. As the three cases were somewhat different, treatment protocols had to be modified as follows: Case 1. Immediate implant placement with healing abutment connection. Case 2. Immediate implant placement with immediate provisionalization. Case 3. Immediate implant placement with Guided Bone Regeneration(GBR). Every implant of these cases was placed in proper position buccolingually, mesiodistally and apicocoronally, The procedures following implantation such as immediate provisionalization and GBR were free of problem. Healing of each case was uneventful. In all cases, treatment outcomes were mostly satisfactory and the results maintained during follow-up periods. However, one case (Case 3) showed some papilla loss due to failure in delicate soft tissue handling during surgery. This papilla loss was compromised by prosthetic means. In conclusion, immediate implant placement in the fresh extraction socket can be a valid and successful option of treatment in aesthetic area. Moreover, this treatment protocol seems to maintain the preexisting architecture of soft and hard tissues in most cases.

• 한국안전학회지
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• 제23권4호
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• pp.13-18
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• 2008

This study deals with finish roll forming by forced displacement can be conceived as a method of eliminating errors in conventional form rolling under constant loads. This method produces a high-precision tooth profile by low-speed form rolling when a high rigid screw or cam is used at the pressurized section. Tooth profile is decided in the beginning of roll forming and ${\delta}_{max}$ mainly increases if the number of roll forming process is increased. Gear class is improved by one or two class after roll forming if the gear has convex type error and pressure angle error in KS 4 class. If the gear have concave type error and pressure angle error and pressure angle error, gear class is not improved in theory, but improved a little in practice. In the finishing roll forming, it inevitably yields both the concaving of tooth profile and plastic deflection of addendum of teeth. Experiments show that the concaving and the plastic deflection are successfully reduced, the accuracy of tooth profile reaches to KS 0 class.