• The Journal of Korean Academy of Prosthodontics
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• v.31 no.1
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• pp.129-150
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• 1993

Since the restoration or masticatory function is the most important aim of implants, it should be substituted for the role of natural teeth and deliver the stress to the bone under the continous load during function. In natural teeth, stress distribution can be obtained through enamel, dentin and cementum and the elasticity of the periodontal ligament play a role of buffering action. In contrast, implant prosthesis has a very unique characteristics that it delvers the load directly to bone through the implant and superstructure. This fact arise the needs to evaluate the stress distribution of the implant in the mechnical aspects, which has a similar role of natural teeth but different pathway of stress. With 3 kinds of implant in prevalent use, 2 types of experimental PEA implant models were made, axisymmetric and 2-dimensional type. In axisymmetric model, the stiffness of the part including the prosthesis and implant which extrude out of bony surface could be calculated with displacement of the superstructure un er 100N vertical load and then damping effects could be determined through this stiffness. In axisymmetric FEA model, load to the bone could be deduced by evaluation the stress distribution of the designed surface under the 100N vertical force and in 2-dimensional model, 100N eccentric vertical load and 20N horizontal loda. The result are as follows. 1. In every implant, stress to the bone tends to be concenturated on the cortical bone. 2. Though the stress of the cancellous bone is larger at the apex of implants, it is less compared with cortical bone. 3. Under 20N horizontal load, stress of the left and right sides of implant shows a symmetrical pattern. But under 100N eccentric vertical load, loaded side shows much larger stress value. 4. In the 1mm interface, stress distribution among implants tend to have a similar pattern. But under 20N horizontal load apposite side of being loaded shows less stress in IMZ. 5. In the case of screw type implant, stress tends to vary along with screw shape. 6. According to the result determined with microstrain, cancellous bone id generally under the condition of overload, while cortical bone is usually within the limitation of physiologic load. 7. In the Branemark implant, maximum stress to the cortical bone is larger than any other implant except for the condition of 20N horizontal force and 0.05mm interface. 8. Damping effects of implants is maximum in IMZ.

• Korean Journal of Applied Biomechanics
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• v.12 no.2
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• pp.1-16
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• 2002

The purposes of this study were to investigate the effects of strength training on the change of ground reaction force for the children with trisomy 21 Down syndrome. The subjects of this study were consisted of eight elementary school students with Down syndrome who participated in the strength training. The strength training was administered by six items such as squat, leg curl, leg extension, toe raise, sit-ups, and hyperextension. For strengthening muscle, each group also was treated by walking for 8 weeks, three times a week, 10-15RM, 3sets, which was based on the principle of progressive overload. For inquiring the effect of strength training, the ground reaction force variables were measured in two phases : before-training and 8 week-after training. The gait of each subject was acquisition using 2 AMTI force platforms set at 100 frequency. The results of this study were as follows: The pattern of vertical, antero-posterior and medio-lateral forces, trajectory of net COP and the timing ratio of reaching the each events were shown variously. So, it is not easy to explain these variables clearly. As the result of strength training, these variables were changed. However, the results of within subjects differ greatly, there was no difference statistically.

• Journal of Intelligence and Information Systems
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• v.13 no.3
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• pp.119-140
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• 2007

Recommender systems enable a user to decide which information is interesting and valuable in our world of information overload. As the recent studies of distributed computing environment have been progressing actively, recommender systems, most of which were centralized, have changed toward a peer-to-peer approach. Collaborative Filtering (CF), one of the most successful technologies in recommender systems, presents several limitations, namely sparsity, scalability, cold start, and the shilling problem, in spite of its popularity. The move from centralized systems to distributed approaches can partially improve the issues; distrust of recommendation and abuses of personal information. However, distributed systems can be vulnerable to attackers, who may inject biased profiles to force systems to adapt their objectives. In this paper, we consider both effective CF in P2P environment in order to improve overall performance of system and efficient solution of the problems related to abuses of personal data and attacks of malicious users. To deal with these issues, we propose a multi-agent framework for a distributed CF focusing on the trust relationships between individuals, i.e. web of trust. We employ an agent-based approach to improve the efficiency of distributed computing and propagate trust information among users with effect. The experimental evaluation shows that the proposed method brings significant improvement in terms of the distributed computing of similarity model building and the robustness of system against malicious attacks. Finally, we are planning to study trust propagation mechanisms by taking trust decay problem into consideration.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.34 no.5
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• pp.571-577
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• 2008

Introduction: Possible etiologic factors associated with bone loss around implants after implantation are surgical trauma, occlusal overload, periimplantitis, presence of micro gap and the formation of biologic distances. Tarnow et al. observed that the crestal bone loss was greater when the distance between the implants was <3mm than when the implants were ${\geq}\;3mm$ apart. The aim of this study was to evaluate the influence of different interimplant distance on marginal bone and crestal bone resorption in the beagle dogs. Materials and methods: The mandibular premolars of 5 dogs were extracted bilaterally. After 12 weeks of healing, each dog received 7 implants. On each side, implants were separated by 2mm (Group 1) and by 5mm (Group 2). After 16 weeks of healing, the dogs were sacrificed. Marginal bone loss was determined through linear measurements made between the implant-abutment junctions and the most coronal portions of the bone in contact with the implant surface. A line was drawn uniting the implant-abutment junctions of the adjacent implants, and a linear measurement was made at the midpoint in the direction of the most coronal peak of the interimplant bone crest to determine the crestal bone loss. Both of them was measured radiologically and histologically. Result and conclusion: In radiological analysis, the mean of marginal bone loss was $1.26{\pm}0.14mm$ for group 1 and $1.23{\pm}0.34mm$ for group 2, the mean of crestal bone loss was $1.10{\pm}0.14mm$ for group 1 and $1.02{\pm}0.30mm$ for group 2. The results were not statistically significant between 2 groups. In histological analysis, the mean of marginal bone loss was $1.63{\pm}0.48mm$ for group 1 and $1.62{\pm}0.50mm$ for group 2, the mean of crestal bone loss was $1.23{\pm}0.35mm$ for group 1 and $1.15{\pm}0.39mm$ for group 2. The differences were also not statistically significant. The clinical significance of this result is that the increase in the crestal bone loss results in the increase in the distance between the base of the interproximal contact of the crowns and the bone crest, and this determines if papilla will be present or absent between implants. Considering this fact, keeping up sufficient interimplant distance is important to minimize crestal bone loss.

• Proceedings of the Korea Society for Industrial Systems Conference
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• 1999.12a
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• pp.121-129
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• 1999

When continuous media are transmitted over the communication networks, asynchrony which can not maintain temporal relationships among packets may occur due to a random transit delay. There exist two types of synchronization schemes ; for guaranteed or non-guaranteed resource networks. The former which applies a resource reservation technique maintains delay characteristics, however, the latter supply a best-effort service. In this paper, I propose a intra-media synchronization scheme to transmit continuous media on general networks not guaranteeing a bounded delay tome. The scheme controls transmission times of the packets by estimating next delay time with the delay distribution. So, the arriving packets may be maintained within a limited delay boundary, and playout will be performed after buffering to smoothen small delay variations. The continually increasing delay due to network overload causes buffer underflow at the receiver. To solve it, the transmitter is required to speed up instantaneously. Too much increase of transmission-rate may cause network congestion. At that time, the transmitter drops the current packet when informed excessive delay from the receiver.

• Journal of KIISE:Databases
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• v.37 no.1
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• pp.22-32
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• 2010

Location-based services have been expanded rapidly in local and overseas markets due to technological advances and increasing applications of wireless internet. Various researches have been made to manage efficiently the location information of moving objects. A basic location-based alert service provides alerting messages automatically when either entering or leaving a specific location and it is expected to become one of the most important location-based services. Location-based alert services require a location polling method to acquire current locations for a large number of moving objects. However, a simple periodical location polling method causes severe system overload because a system should keep updating location information of the moving objects ceaselessly. Most location polling algorithms for location-based alerting services are not suitable for mobile users with dynamic and unsteady moving patterns. In this paper, we propose an improved location polling algorithm for location-based alerting services to reduce the amount of location information acquisition and therefore, to decrease the system load. Various experiments show that the proposed algorithm outperforms other algorithms.

• Journal of Korean Public Health Nursing
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• v.12 no.1
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• pp.55-74
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• 1998

In the past most major accidents resulted in death, but today there is a dramatic increase in the number of people who survive such accidents but who are left with permanent injury. Particularly, children who are inquisitive about their surroundings but immature in their ability to assess danger, are more vulnerable to accidents and their causes as well as to determine attitudes towards prevention. The main objective of the study was to assess the effectiveness of using an accident prevention manual for accident for accident prevention education. The study was a quasi-experimental study using a questionnaire format. The subjects of the study were 393 mothers of children attending six day care centers in Seoul. Data collection was done between May 1 and June 15, 1997. The tools used for the study were a questionnaire developed the researchers and a manual for accident prevention. The collected data were analyzed using SPSS. The results of the study are as follows: 1. Types of accidents included stabbing, bums, falls from heights, choking, falls on slippery surfaces, traffic accidents, drowning, poisoning, and electrical shock in that order of frequency. 2. The main causes of accidents in children were from cosmetics and household medications. 3. The most frequent locations of accidents in the home were the bathroom, kitchen, and stairways in that order. 4. For $90.4\%$ of children safety seats were not used when the ridding in a car. 5. In examining the parents' accident prevention practices, it was found that many parents used only . one electrical outlet for many appliances, tending to overload the electricity lines and that they were not practically concerned bout the flammability of children's pajamas, indicating a less than positive attitude towards fire prevention. 6. The parents had not provided their children with any instruction on accident prevention or on what to do after an accident had occurred. 7. After the use of pamphlet in an accident prevention education program, it was found that there was a statistically significant difference in the degree to which children carried out safety measures (t=14.96, p=.000) and in their safety habits (t=-1.67, p<.1) indicating an effectiveness in this method of education. The results of this study showed that there are many things in a child's environment that can cause accidents and that the possibility of an accident occurring is high. So nurses looking after children should be aware of the need for safety education to prevent accidents in the home and plan to provide appropriate educational material to help parents with this education.

• Journal of Korea Multimedia Society
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• v.7 no.8
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• pp.1066-1077
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• 2004

Dramatic increase in the number of Internet users want highly qualified service of continuous media contents on the web. To solve these problems, we present two network caching schemes(PPC, PPCwP) which consider the characteristics of continuous media objects and user access pattern in this paper. While there are plenty of reasons to create rich media contents, delivering this high bandwidth contents over the internet presents problems such as server overload, network congestion and client-perceived latency. PPC scheme periodically calculates the popularity of objects based on the playback quantity and determines the optimal size of the initial fraction of a continuous media object to be cached in proportion to the calculated popularity. PPCwP scheme calculates the expected popularity using the series information and prefetches the expected initial fraction of newly created continuous media objects. Under the PPCwP scheme, the initial client-perceived latency and the data transferred from a remote server can be reduced and limited cache storage space can be utilized efficiently. Trace-driven simulation have been performed to evaluate the presented caching schemes using the log-files of iMBC. Through these simulations, PPC and PPCwP outperforms LRU and LFU in terms of BHR and DSR.

• The KIPS Transactions:PartA
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• v.13A no.1 s.98
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• pp.45-52
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• 2006

To perform on-line maintenance for Distributed Information System, it is indispensable to disseminate files to participant nodes in the network. When users' requests for file deployment occur simultaneously in a short period a deployment server falls into overload phase, which is often called Flash Crowds. h common solution to avoid Flash Crowds is to increase hardware capacity. In this paper, we propose a software solution based on P2P, which does not cost any additional expense. In the proposed solution, nodes in the network are grouped into subnetworks one of which is composed of only neighboring nodes. In each subnetwork, copies of deployment files can be transferred to each other. Consequently, it brings about the effect of load balancing in deployment server. To raise the effectiveness, target files for deployment are packed into one package. Before being transferred, each package is divided into multiple equal-sized segments. A deployment server in a normal phase transmits a package requested from nodes in segment units. However a deployment server is overloaded, if segments already exist in the subnetwork participant nodes in the subnetwork receive necessary segments from neighboring nodes. In this paper, we propose data structures and algorithm for this approach and show performance improvement through simulation.

• The KIPS Transactions:PartD
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• v.9D no.5
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• pp.801-812
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• 2002

On-line reorganization in a shared nothing database cluster is crucial to the performance of the database system in a dynamic environment like WWW where the number of users grows rapidly and changing access patterns may exhibit high skew. In the existing method of on-line reorganization have a drawback that needs excessive data migrations in case more than two nodes within a cluster have overload at the same time. In this paper, we propose an advanced B$^{+}$ tree based on-line reorganization method that solves data skew on multi-nodes. Our method facilitates fast and efficient data migration by including spare nodes that are added to cluster through on-line scaling. Also we apply CSB$^{+}$ tree (Cache Sensitive B$^{+}$ tree) to our method instead of B$^{+}$ tree for fast select and update queries. We conducted performance study and implemented the method on Ultra Fault-Tolerant Database Cluster developed for high scalability and availability. Empirical results demonstrate that our proposed method is indeed effective and fast than the existing method. method.