• Journal of Ecology and Environment
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• v.44 no.3
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• pp.126-142
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• 2020

Background: Most of the Pinus densiflora forests, occupying the largest area, have been restored in South Korea since the 1970s. As young pioneer forests, the succession process is under way. Since the forests are distributed nationwide and are vulnerable to disturbances, the process may differ depending on the geography and/or site conditions. Therefore, we reviewed the direction, the seral communities, and the late-successional species of progressive and disturbance-driven succession nationwide in the cool-temperate zone through meta-analysis and empirical observations. Main text: As a result of a meta-analysis of the direct succession and vertical structure, we found that the P. densiflora forest is in a directionally progressive succession, changing to the broadleaved forest after forming a mixed forest with its overwhelming successor, Quercus species (particularly Q. mongolica and Q. serrata). In dry stands in a relative sense, the Quercus species was favored occupying over 80% of the abundance of the succeeding species. Therefore, in dry stands, it is presumed that Quercus-dominated stage would last for a long time due to the current dominance and long life span, and eventually, it settles as Quercus-broadleaved forest with a site change. Contrary to this, it is presumed that in mesic stands where Quercus species do not occur or have low abundance, the late-successional broadleaved species settle early to form a co-dominant forest with multiple species. Due to geographical limits, the species composition of the two late-successional forests is different. Disturbances such as insect pests and fire retrogressed vulnerable P. densiflora forest for a while. However, it was mostly restored to the Quercus forest and is expected to be incorporated in the pathway of the dry stand. Conclusions: We revealed the succession process of P. densiflora forests according to geography and moisture and found that stand moisture had a decisive effect on the species and abundance of the successor. Although the P. densiflora forest is undergoing structural changes, the forest is still young; so within a few decades, physiognomy is not likely to change. Therefore, the decrease in the forest area may be due to other causes such as disturbances and forest conversion rather than due to succession.

• Smart Structures and Systems
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• v.25 no.4
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• pp.487-499
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• 2020

This paper proposes a novel approach to model updating for a large-scale cable-stayed bridge based on ambient vibration tests coupled with a hybrid metaheuristic search algorithm. Vibration measurements are carried out under excitation sources of passing vehicles and wind. Based on the measured structural dynamic characteristics, a finite element (FE) model is updated. For long-span bridges, ambient vibration test (AVT) is the most effective vibration testing technique because ambient excitation is freely available, whereas a forced vibration test (FVT) requires considerable efforts to install actuators such as shakers to produce measurable responses. Particle swarm optimization (PSO) is a famous metaheuristic algorithm applied successfully in numerous fields over the last decades. However, PSO has big drawbacks that may decrease its efficiency in tackling the optimization problems. A possible drawback of PSO is premature convergence leading to low convergence level, particularly in complicated multi-peak search issues. On the other hand, PSO not only depends crucially on the quality of initial populations, but also it is impossible to improve the quality of new generations. If the positions of initial particles are far from the global best, it may be difficult to seek the best solution. To overcome the drawbacks of PSO, we propose a hybrid algorithm combining GA with an improved PSO (HGAIPSO). Two striking characteristics of HGAIPSO are briefly described as follows: (1) because of possessing crossover and mutation operators, GA is applied to generate the initial elite populations and (2) those populations are then employed to seek the best solution based on the global search capacity of IPSO that can tackle the problem of premature convergence of PSO. The results show that HGAIPSO not only identifies uncertain parameters of the considered bridge accurately, but also outperforms than PSO, improved PSO (IPSO), and a combination of GA and PSO (HGAPSO) in terms of convergence level and accuracy.

• Journal of the Korea Concrete Institute
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• v.21 no.5
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• pp.619-628
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• 2009

To predict the time-dependent behavior of concrete structures, the models which describe the time-dependent characteristics of concrete, i.e. creep and shrinkage are required. However, there must be significant differences between the displacements that are obtained using the given creep and shrinkage models and the measured displacements, because of the uncertainties of creep and shrinkage model itself and those of environmental condition. There are some efforts to reduce these error or uncertainties by using the model which are obtained from creep test for the concrete in construction site. Nevertheless, the predicted values from this model may be still different from the actual values due to the same reason. This study aimed to propose a method of estimating the creep coefficient from the measured displacements of concrete structure, where creep model uncertainty factor was considered as an error factor of creep model. Numerical validation for double composite steel box and concrete beam showed desirable feasibility of the presented method. Consideration of the time-dependent characteristics of creep as one of the error factors make it possible to predict long-term behaviors of concrete structures more realistically, especially long-span PSC girder bridges and concrete cable-stayed bridges of which major problem is the geometry control under construction and maintenance.

• 한국유가공학회:학술대회논문집
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• 2004.06a
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• pp.21-39
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• 2004

Fermented milks have been recognized as healthy foods since ancient times, but those using intestinal bacteria such as Bifidobacterium and lactic acid bacteria (LAB) are even more valuable from the standpoint of view of maintaining health. They have also now come to be recognized as important in the field of preventive medicine. Although advances in the medical sciences in the last 50 years have significantly increased the human lift span, an unfortunate fact is that many of us are now living long enough to experience chronic disorders such as coronary heart disease, hypertension, osteoporosis, diabetes and cancer. In recent years there has been renewed interest in health promotion and disease prevention by incorporating probiotic bacteria into foods to counteract harmful bacteria in the intestinal tract. Therefore, there are now a wide variety of commercial products containing prospective probiotics that claim health-promoting effects, such reductions in large botvel carcinogens and mutagens, antitumor properties, cholesterol-lowering effects, increased lactose digestion, relief from con-stipation, stimulation of immunocomponent cells and enhancement of phagocytosis. Two well-known representative probiotic is LAB and Bifidobaclerium. Traditional probiotic dairy strains of LAB which have been designated as GRAS (Generally Recognized As Safe) bacteria have a long history of safe use and most strains are considered comestible microorganisms with no pathogenic potential. Accordingly, there is considerable interest in extending the range of foods containing probiotic organisms from dairy foods to infant formulas, baby foods, and pharmaceuticals. In addition, the ingestion of probiotics, prebiotics, and symbiotic as wll as combinations of pro- and prebiotics has recently aroused renewed interest as enhancing the beneficial relationship between the host and intestinal microflora in both healthy and diseased indivisuals. Non-communicable chronic diseases such as cancer, cerebral hemorrhage, is chemic heart disease, and diabetes mellitus has recently been recognized as adult diseases in Japan as well as other countries. and are considered to be inevitably associated with aging. These diseases occur as a result of individual life styles. The Japanes Government. Ministry of Health, Labor and Welfare has proposed substituting the term 'adult diseases' with 'lifestyle-related diseases'. It has emphasized the importance of prevention rather than treatment. since the well-known increase in the elderly population in Japan is predicted to result in a variety of socioeconomic problems. n this lecture on the Present status of fermented milk products in Japan, I will report a strategy for the development of fermented milk products in Japan from the standpoint of view of research in Japan on LAB and Bifidobacteria. They could play an important role in preserving human health by controlling intestinal microflora capable of producing toxic effects on the host.

• The Journal of Korean Academy of Prosthodontics
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• v.57 no.3
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• pp.288-295
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• 2019

Passive fit of prosthesis is an essential property of implant supported prosthesis for long term success and minimization of complications. And the property is determined mostly by fabrication procedure. There were limitations of extensive implant prosthesis because conventional casting method generate contraction error of long span prosthesis. However, Computer-aided design/Computer-aided manufacturing (CAD/CAM) technology of 3D printing and milling metal framework can overcome those limitations. This case is a full mouth rehabilitation using extensive implant fixed prosthesis. Removable interim prosthesis was made for esthetic, functional evaluation and a guide for implant insertion. After the insertion, implant fixed interim prosthesis was delivered. After additional evaluation and adjustment, final prosthesis was designed with CAD, the fabricated with CAM. Milling technique was used for anterior screw type implant superstructure and 3D printing technique was used for the anterior and posterior implant copings. Fit of the final restoration was favorable. The practitioner and patient were both esthetically and functionally satisfied with the final result.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.5A
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• pp.407-415
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• 2010

In Korea, more than 90% of the total number of steel bridges built for 40~70 m span length is a steel box-girder bridge type. A steel box-girder bridge is suitable for long span or curved bridges with outstanding flexural and torsional rigidity as well as good constructability and safety. However, a steel box-girder bridge is uneconomical, requiring many secondary members and workmanship such as stiffeners and ribs requiring welding attachments to flanges or webs. Therefore, in US and Japan, a plate girder bridge, which is relatively cheap and easy to construct is generally used. One type of the plate girder bridge is the two- or three-main girder plate bridge, which is a composite plate girder bridge that minimizes the number of required main girders by increasing the distance between the adjacent girders. Also, for the simplification of girder section, the stiffener which requires attachment to the web is not required. The two-main steel girder plate bridge is a representative type of plate girder bridges, which is suitable for bridges with 10 m effective width and has been developed in the early 1960s in France. To ensure greater safety of two- or three-main girder plate bridges, a larger steel section is used in the bridge domestically than in Europe or Japan. Also, the total number of two- or three-main girder plate bridge constructed in Korea is significantly less than the steel box girder bridge due to a lack of designers' familiarity with more complex design detailing of the bridge compare to that of a steel box girder bridge design. In this study, a new construction method called Turn Over method is proposed to minimize the steel section size used in a two- or three-main girder plate bridge by applying prestressing force to the member using confining concrete section's weight to reduce construction cost. Also, a full scale 20 m Turn Over girder specimen and a Turn Over girder bridge specimen were tested to evaluate constructability and structural safety of the members constructed using Turn Over process.

• Journal of Korean Society of Steel Construction
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• v.16 no.6 s.73
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• pp.725-736
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• 2004

A new type of girder, called steel-confined prestressed concrete girder (SCP girder), has been developed, which maximizes the structural advantages of concrete, steel, and PS tendon, and improves on the shortcomings of steel plate girder, PSC I-girder, and preflex girder bridge for use in the construction of middle- or long-span bridges. To verify the propriety of design, structural safety, and applicability of this girder, a static load test was carried out (Kim et al.., 2002). Since the main damage typically sustained by steel bridges results from the fatigue caused by the repetition of traffic loads, fatigue safety must therefore be guaranteed in applying the SCP girder in the construction of real bridges. In this study, a fatigue test was carried out to investigate fatigue behavior and provide basic data for fatigue design. Based on the fatigue test, the fatigue safety of the girder was estimated. For the fatigue test, 10-m specimens were designed for a standard-design truckload (DB-24). A static load test was also performed before the fatigue test to analyze the structural behavior of the specimens. After the fatigue test, outer steel plates were removed to observe the condition of the concrete in the girder.

• Journal of Korean Society of Steel Construction
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• v.20 no.5
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• pp.609-616
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• 2008

Recently, many ocean bridges that connect land to island or island to island have been constructed along with the improvement of the nation's economy. Long-span bridges can be categorized as suspension bridge, cable-stayed bridge, arch bridge and truss bridge. In this study, correction with respect to construction error can be presented on site through the monitoring of the cable tension change of real structure for four major construction stages so that construction accuracy, including the management of profiles, can be improved. A vibration method, the so-called indirect method that uses the cable's natural frequency changes from the acceleration sensor installed on the cable, is applied in measuring cable tension. In this study, the estimation formula for the effective length of cable with damper is presented by comparing and analyzing between actual measurement and analysis result for the change of the cable's effective length. By the way, it is known that the reliability of estimating cable tension by applying the former method that uses the net distance from damper to anchorage is low. Therefore, for future reference of the maintenance stage, the presented formula for estimating the effective length of cable can be used as a reference for the rational decision-making, such as the re-tensioning and replacement of cable.

• Journal of Korean Society of Steel Construction
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• v.27 no.6
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• pp.503-511
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• 2015

In long span steel structure, the plate girder reinforced with stiffeners are commonly used. When choosing the cross section with deep depth of girder as well as narrow width, however, out of plane buckling can be a problem due to web slenderness. In an effort to solve this issue, current study determined the applicability of using corrugated web girder with deep depth as bending member, which is generally being utilized in both factory and warehouse nationwide. To accomplish this, we performed the loading test of H-shaped beam with sinusoidal corrugated web. Corrugated web CP-2.3 specimen exhibited 12% less maximal bending strength but CP-3.2 specimen exerted 24% increase in strength compared to plate web P-4.5. this result indicates that corrugated web provides enough strength even with unfavorable width-thickness ratio of plate. And bending as well as shear strength estimated by the Eurocode (EN 1993-1-5) were compared with both bending strength by loading test and shear strength estimated by KBC2009. In case of eurocode, increase in plate thickness did not help in bending performance improvement. moreover, shear performance was sensitive to the thickness of the web folds and the shape of the web plate.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.1A
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• pp.1-10
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• 2012

Along with the development of coasts, islands and mountains, the demand of long-span bridges increases which, in turn, brings forth the construction of cable-supported bridges like suspension and cable-stayed bridges. There are various types of statically indeterminate structures widely applied that supported the main girder with stay cables, main cables, hanger cables with aesthetic structural appearance. As to the cable-supported bridges, the health monitoring of a bridge can be identified by measuring tension force on cable repeatedly. The tension force on cable is measured either by direct measurement of stress of cable using load cell or hydraulic jack, or by vibration method estimating tension force using cable shape and measured dynamic characteristics. In this study, a method to estimate dynamic characteristics of hanger cables by using a digital image processing is suggested. Digital images are acquired by a portable digital camcorder, which is the sensor to remotely measure dynamic responses considering convenient and economical aspects for use. A digital image correlation(DIC) technique is applied for digital image processing, and an image transform function(ITF) to correct the geometric distortion induced from the deformed images is used to estimate subpixel. And, the correction of motion of vision-based measurement system using a fixed object in an image without installing additional sensor can be enhanced the resolution of dynamic responses and modal frequencies of hanger cables.