• Journal of Advanced Marine Engineering and Technology
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• v.17 no.4
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• pp.38-48
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• 1993

A study on friction welding of stainless steel bar(SUS431) to chrome molybdenum steel bar(SCM21) was accomplished experimentally through analysis for relations among friction welding conditions, tension test, hardness test, microstructure test and acoustic emission test. The results obtained are summarized as follows ; 1. Through friction welding of SUS431 bar to SCM21 bar, the optimum welding condition by considering on strength and toughness was found to be the range of heating time of 3-5 sec when the number of rotating speed of 2000rpm, heating pressure of 10kg/$mm^2$, and upsetting time of 4 sec. 2. Quantitative ralationship was identified between heating time($T_1$, sec) and tensile strength (${\sigma},\;kgf/mm^2$) of the friction welded joint and the relation equation is $\sigma$=52.62$T_1{^{0.06}}$. 3. Through AE test, quantitative relationship was confirmed between heating time($T_1$, sec) and total AE(N, counts) during welding, and the relation is computed as follows ; N=30413.6$e^{0.06T1}$. 4. It was confirmed that the quantitative ralationship exists between the tensile strength of the welded joints and AE cumulative counts. And the relation is computed as the following ; ${\sigma}$=16.37(ln N)- 116.4. 5. When ONZ=36500-41500 counts by $OT_1Z$=3~5sec, it was identified by experiment that the range of welded joint tensile strength is 55.6-57.7kgf/$mm^2$/ whose joint efficiency is more than 100%, and it was experimentally confirmed that the real-time nondestructive quality(strength) evaluation for the friction welded joints could be possible by acoustic emission technique.

• Transactions of the Korean Society of Mechanical Engineers
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• v.7 no.3
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• pp.263-269
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• 1983

Underwater welding by a gravity arc welding process was investigated by using six types of coated electrodes and SM41A steel plates of 10 mm thickness as base metal and it was ascertained that this process may be put to practical use. Main results obtained are summarized as follows: 1. Angle of electrode affects no influence on bead appearance and the proper range of welding current and diameter of electrode for the high titanium oxide type is relatively wider than that for the ilmenite type. And the lime titania type, high titanium oxide type and ilmenite type of domestic coated arc welding electrodes of .phi.4 mm could attain the soundest underwater welded joints which contain no welding imperfection. 2. According to macro-structure, micro-structure and hardness distribution inspectionson underwater welded joint, the area between the HAZ and the surface of the weld in neighbourhood of the bond has the maximum hardness value. The structure of these parts is martensite and bainite. Other parts contain mocro-ferrite, micro-pearlite structure, which contain soundness of welded joint free from weld imperfection. 3. On consideration of both tensile strength of more than 100% joint efficiency and sufficient impact value, the welding condition which can get optimal welding strength is heat input of 1,400-1,500 J/mm, current of 200-215 ampere (voltage of 32-33 volts) in the case of lime titania type electrode. 4. Underwater welding strength (tensile strength, impact strength) depends on heat input (or current) quantitatively and they have the relationship of parabolic function. Each experimental equation has a high reliability and its percent of mean error is 4.14%. 5. It is suggested that the optimal design of weld strength by welding condition (current, heat input) could be utilized for a quality control of underwater welding.

• The Journal of Korean Academy of Prosthodontics
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• v.34 no.3
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• pp.501-532
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• 1996

This study investigated the effects of cantilever length, location and load condition on stress distribution developed in the implants, prostheses and supporting tissues. The osseointegrated prostheses with two 10mm Branemark implants at 2nd premolar and 1st molar sites with cantilever extensions at 1st premolar, 2nd and 3rd molar sites were constructed. Under 100N, 200N of vertical and $45^{\circ}$ oblique loads at the cantilever pontics, stress distribution patterns and displacement were analyzed with three dimensional finite element method. The results were as follows : 1. The stress was concentrated at the joint of the cantilever pontic and implant superstructure, the neck of implant and the ridge crest near the cantilever But there was little load transfer to the lower supporting tissues of implants. 2. The implant near the cantilever was displaced inferiorly while the implant far from the cantilever was displaced superiorly. In horizontal direction the implants were displaced to the direction where the loads were applied, except the apexes of the implants. 3. In case of anterior cantilever, the stress and displacement were higher than the prosthesis connected with natural tooth. 4. The stress developed in the posterior cantilevered type was higher than in the anterior cantilevered type. The greastest stress was concentrated at the ridge crest near the posterior cantilever. 5. The longer the cantilever, the more the stress was developed and was concentrated at the joint of the cantilever pontic and implant superstructure. 6. Under oblique load, the stress was concentrated at the necks of implants and the ridge crests, but decreased at the joint of the cantilever pontic and implant superstructure than under vertical load.

• Journal of the Korean Geotechnical Society
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• v.33 no.11
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• pp.83-95
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• 2017

This study examined the magnitude and distribution of earth pressure on the excavation wall in jointed rock mass by considering different groundwater conditions under various rock types, joint inclination angles, and earth pressure coefficients. Based on a physical model test (Son and Park, 2014), extended studies were conducted considering rock-structure interactions based on the discrete element method, which can consider the joints characteristics of rock mass. The results showed that the earth pressure was highly influenced by the groundwater condition as well as the rock type, joint inclination angle, and earth pressure coefficient. The results were also compared with Peck's earth pressure for soil ground, and clearly showed that the earth pressure in jointed rock mass can be greatly different from that in soil ground.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.3
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• pp.151-165
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• 2021

Grouting, which is applied for the increase of ground strength and the decrease of permeability, is complex process because of several reasons, so the process needs to be elaborated. Injection process in consideration of ground condition and optimization of grouting sequence is essential. In this study, GIN (Grouting Intensity Number), multiple of injected grout volume and pressure, is revised to consider injection pressure reduction and joint opening during grouting process. A revised GIN process is evaluated through a field test. A revised GIN, considering ground condition, injection pressure, follows GIN envelope and produces rational grouting process. The result of a revised GIN reduces permeability of the ground in the order of 10^-1~10^-2 cm/sec.

• Journal of Microbiology and Biotechnology
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• v.27 no.12
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• pp.2180-2189
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• 2017

Psychrophilic phytases suitable for aquaculture are rare. In this study, a phytase of the histidine acid phosphatase (HAP) family was identified in Morchella importuna, a psychrophilic mushroom. The phytase showed 38% identity with Aspergillus niger PhyB, which was the closest hit. The M. importuna phytase was overexpressed in Pichia pastoris, purified, and characterized. The phytase had an optimum temperature at $25^{\circ}C$, which is the lowest among all the known phytases to our best knowledge. The optimum pH (6.5) is higher than most of the known HAP phytases, which is fit for the weak acidic condition in fish gut. At the optimum pH and temperature, MiPhyA showed the maximum activity level ($2,384.6{\pm}90.4{\mu}mol{\cdot}min^{-1}{\cdot}mg^{-1}$, suggesting that the enzyme possesses a higher activity level over many known phytases at low temperatures. The phytate-degrading efficacy was tested on three common feed materials (soybean meal/rapeseed meal/corn meal) and was compared with the well-known phytases of Escherichia coli and A. niger. When using the same amount of activity units, MiPhyA could yield at least $3{\times}$ more inorganic phosphate than the two reference phytases. When using the same weight of protein, MiPhyA could yield at least $5{\times}$ more inorganic phosphate than the other two. Since it could degrade phytate in feed materials efficiently under low temperature and weak acidic conditions, which are common for aquacultural application, MiPhyA might be a promising candidate as a feed additive enzyme.

• Journal of the Korean Geotechnical Society
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• v.30 no.2
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• pp.43-52
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• 2014

This paper examined the effect of step-wise excavation depth on the earth pressure against an excavation wall in rock mass. Numerical parametric studies were conducted based on the Discrete Element Method (DEM) to carry out the problems in rock mass. Controlled parameters included step-wise excavation depth, rock types, and joint conditions (joint shear strength and joint inclination angle). The magnitude and distribution characteristics of the induced earth pressure in a jointed rock mass were investigated and compared with Peck's earth pressure for soil ground. The results showed that the earth pressure against an excavation wall in rock mass were highly affected by different rock and joint conditions, and the effect of step-wise excavation depth increased as a rock type is deteriorated more. In addition, it was found that the earth pressure against an excavation wall in rock mass might be considerably different from Peck's empirical earth pressure for soil ground.

• Journal of the Korea Computer Graphics Society
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• v.1 no.2
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• pp.201-212
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• 1995

This paper presents a new method of dynamics-based synthesis of bipedal, especially human, walking. The motion of the body at a time point is determined by ground reaction force and torque under the support foot and joint torques of the body at that time point. Motion synthesis involves specifying conditions that constrain ground reaction force and torque, and joint torques so that a given desired motion may be achieved. There are conditions on a desired motion which end-users can think of easily, e.g. the goal position and orientation of the swing foot for a single step and the time period of a single step. In this paper, we specify constraints on the motion of the support foot, which end-users would find difficult to specify. They are constraints which enforce non-sliding, non-falling, and non-spinning the support foot. They are specified in terms of joint torques and ground reaction force and torque. To satisfy them, both joint torques and ground reaction force and torque should be determined appropriately. The constraints on the support foot themselves do not give any good clues as to how to determine ground reaction force and torque. For that purpose, we specify desired trajectories of the application point of vertical ground reaction force (ground pressure) and the application point of horizontal ground reaction (friction) force. The application points of vertical pressure and friction force are good control variables, because they are indicators to kinds of walking motions to synthesize. The synthesis of a bipedal walking motion, then, consists of finding a trajectory of joint torques to achieve a given desired motion, so that the constraints are satisfied under the condition of the prescribed center of pressure and center of friction. Our approach is distinguished from many other approaches, e.g. the inverted-pendulum approach, in that it captures and formulates dynamics of the support foot and reasonable constraints on it.

• The Journal of Engineering Geology
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• v.13 no.2
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• pp.193-205
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• 2003

Fine grained granite, porphyritic granite and biotite granite together with intruded and extruded andesitic rocks are distributed in the study area which is bounded by the Yangsan and Dongrae faults. A new domestic road is being constructed along the area between the two major faults. The NNE trending Bupki fault and NE trending Myungkog fault are also developed within the area cross the road. The sheeting joints with dips of less than 30 degrees are only developed in the area of granite outcrop. High angle joints can be divided into 3 sets, such as, NE trending, NW trending and nearly EW trending joints. The joint space is mostly more than 20cm and the joint compressive strength is more than 100 MPa. These data show that even though the study area is situated between large faults, the ground condition is good because the damage zone of the Yangsan and Dongrae faults is relatively narrow.

• The Academic Congress of Korean Shoulder and Elbow Society
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• 2008.03a
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• pp.170-170
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• 2008

Synovial chondromatosis is an uncommon condition, and the involvement of the shoulder joint is rare. A 15 year old female patient presented to author's institution for right shoulder pain. We checked the plain radiographs and MRI. And they showed that a diagnosis of synovial chondromatosis in the shoulder, and they also demonstrated that the disease involved the bicipital tendon sheath as well as glenohumeral joint. We removed all loose bodies with total synovectomy by arthroscopic procedure, and a mini-open procedure for the lesions of biceps tendon sheath. Arthroscopic treatment affords excellent visualization of the shoulder joint with less morbidity. However, with current arthroscopic techniques, it is difficult to manage the synovial chondromatosis of biceps tendon in bicipital groove. The authors suggest that the complete elimination of synovial chondromatosis involving shoulder requires a mini-open procedure for the lesions of biceps tendon sheath in addition to the arthroscopic resection of the affected synovium and loose body removal in the glenohumeral joint.