• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.20 no.1
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• pp.113-124
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• 1990

For the study of the influence of kilovoltage and exposure time on radiographic density and contrast, we measured radiographic density of aluminum step wedge which composed of contiguous 8 steps wedges of 2-16㎜ thickness with densitometer. Aluminum step wedge was radiographed on Kodak ultraspeed DF-58 and Ektaspeed EP-21 film with range of 60-90 kVp and 5-60 impulse and subject contrast of aluminum step wedge with constant radiographic density and image contrast percentage without radiographic density was evaluated. Then we evaluated the film quality of teeth and their surrounding structure according to the change of kVp and exposure time by score rating method. The obtained results were as follows: 1. Radiographic density was related to the change of kilovoltage, especially in increased exposure time. 2. With constant radiographic density, subject contrast of thin aluminum step wedges was greater in low kilovolt age than high kilovoltage, but kilovolt age had not great influence on subject contrast of thick aluminum step wedge. On the other hand, radiographic density difference between 2mm and 16mm aluminum step wedge was decreased according to in- creasing kilovoltage. 3. Without constant radiographic density, image contrast percentage was decreased with increasing kilovoltage, but was not related with the change of exposure time. 4. Radiographic contrast of teeth and their surrounding structure which was taken with the range of 60-90 kVp and 6-30 impulse had not great influence on film quality.

• Radiation Oncology Journal
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• v.6 no.2
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• pp.155-161
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• 1988

The usefulness of hypertermia for cancer therapy have well been established. The purpose of the present investigation was to ascess the effect of step-up $(42^{\circ}{\rightarrow}44^{\circ}C$ sequence) and step-down $(44^{\circ}{\rightarrow}42^{\circ}C$ sequence) heating on the skin of the hind foot of the mouse. Hyperthermic treatments were given by immersion the hind foot of the mouse in circulating water baths. Skin response was studied by the leg reaction, which was scored according to a numerical scoring system proposed by Urano et al (1980). The results were as follows 1. The skin damage of $44^{\circ}C$ control group was more severe than $42^{\circ}C$ control group (P<0.05), except for 15 min. heating group. 2. The Skin damage of step-down group was more severe than step-up group (P<0.05). 3. The skin damage of $44^{\circ}C$ control group was more severe than step-up group when there is no difference in $44^{\circ}C$ heating time of step-up group from $44^{\circ}C$ control group (P<0.05). 4. In step-down group, the skin damage was more severe than $44^{\circ}C$ control group after preheating 45 min at $44^{\circ}C$ (P<0.05). Therefore, the above findings suggest the normal tissue damage by step-up heating was correlated with heating time of post step-up. The dropping of heating temperature in late phase had more severe damage of the skin than that in early phase during hyperthermia, and so contineous control of satisfactory temperature should be considered as the one of the most important factor for prognosis, complications of clinical hyperthermia

• Journal of Nutrition and Health
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• v.42 no.2
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• pp.158-170
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• 2009

This study was conducted to examine the usefulness of adding final probing step (step3) in dietary assessment by 24-hour recall method among Korean adults. One-hundred fifty five adults (37 males and 118 females) above 30 years of age who visited hospitals for health examination were recruited at three hospitals in Korea. One day dietary intake was obtained using 24-hour recall method from each subject. Dietary interview was conducted in 3 steps, (1) quick list of foods eaten during the previous day, (2) detailed information of all the foods eaten, (3) the final probing for any items forgotten. Items added at the step3 were identified and contributions of energy and nutrient intakes were calculated. The average duration of interview was 10.5 min, and time spent for each step was 4.12 minute for step 1, 5.62 minute for step 2, and 38 second for step 3. The average number of dishes reported by the subjects added at the step 3 was 2.2. (Males = 2.6, Females = 1.6) Frequently reported dishes in the step 3 were Beverage, Tea, alcohol (37.1%) and Fruits (31.8%). From mean total energy intake of 1,589 kcal (Men = 1,846 kcal, Women = 1,509 kcal), 179 kcal (11.3%) was added at the step 3. In the step 3, nutrient intakes increased significantly except retinol in total subjects and except retinol and cholesterol in males but all nutrients increased significantly in females. The final probing step can add significant information on intakes of foods and many nutrients with only about 38 seconds of interview time. Confirmation of the results with larger samples of different age groups is needed.

• Proceedings of the IEEK Conference
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• 1998.10a
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• pp.1175-1178
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• 1998

we propose the Walsh-Hadamard Transform adaptive filter with time-varying step size. The performance of the proposed algorithm is evealuated in system identification where computer simulations are performed for both time-invariant and time-varying system. It is shown that the proposed algorithm produces good results compared with similar algorithms under different conditions, particularly in case of time-varying circumstance.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.199-203
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• 1995

The technology of Semi-Solid Forging (SSF) has been actively developed to fabricate near-net- shape products using light and hardly formable materials, the SSF process is composed of slug heating, forming, compression holding and ejecting step. After forming step in SSF, the slug is compressed during a certain holding time in order to be completely filled in the die cavity and be accelerated in solidification rate. The compression holding time that can affect mechanical properties and shape of products is important to make decision, where it is necessary to find overall hert transfer coefficeient properly which has large effect on heat transfer between slug and die. This paper presents the procedure to predict compression holding time of octaining the final shaped part with information of temperature and solid fraction for a cylindrical slug at compression hoiding step in closed-die compression process using heat transfer analysis considering latent heat by means of finite element method. The influence of the predicted compression hoiding time on mechanical properties of products is finally investigated by experiment.

• Computational Structural Engineering
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• v.6 no.4
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• pp.83-88
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• 1993

A time-discontinuous Galerkin method based upon using a finite element formulation in time has evolved. This method, working from the differential equation viewpoint, is different from those which have been generally used. They admit discontinuities with respect to the time variable at each time step. In particular, the elements can be chosen arbitrarily at each time step with no connection with the elements corresponding to the previous step. Interpolation functions and weighting functions are taken to be discontinuous across inter-element boundaries. These methods lead to a unconditional stable higher-order accurate ordinary differential equation solver.

• Journal of computational fluids engineering
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• v.1 no.1
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• pp.26-34
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• 1996

The performance of the SIMPLE, SIMPLE-C and PISO algorithms for the treatment of the pressure-velocity coupling in fluid flow problems were examined by comparing the computational effort required to obtain the same level of the convergence. Example problems are circular duct and 90-degree bent square-duct. For circular duct case, laminar and turbulent flow were computed. For 90-degree bent square-duct case, laminar flow was simulated by the time-marching method as well as the iterative method. The convergence speed of the other two algorithms are not always superior to SIMPLE algorithm. SIMPLE algorithm is faster than SIMPLE-C algorithm in the simple laminar flow calculations. The application of the PISO algorithm in three dimensional general coordinates is not so effective as in two-dimensional ones. Since computational time of PISO algorithm is increased at each time step(or iterative step) in three dimension, the total convergence speed is not decreased. But PISO algorithm is stable for large time step by using time marching method,.

• Proceedings of the KIEE Conference
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• 2004.11b
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• pp.14-16
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• 2004

A DC railway system has low feeder voltage, The remote fault current can be smaller than the current of load starting. So it is important to discriminate between the small fault current and the load starting current. The load starting current increases step by step but the fault current increases all at once. As for the load starting current, the time constant of load current at each step is much smaller than that of the fault current. To detect faults in DC railway systems, an algorithm using the time constant calculated by the method of least squares was presented. But, It have a weakness about harmonic to calculate time constant. So in this paper, new protection algorithm for DC railway systems using estimation of time constant based on fourier transform was presented.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.1181-1184
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• 1996

As usual systems, robot manipulators have also physical constraints for operating. It is a difficult problem that we operate manipulator in the minimal time under these constraints. In this paper, we solve this problem dividing it into two steps. In the first step, we find the minimal time trajectories by optimizing qubic polynomial joint trajectories using evolutionary algorithms. In the second step, we optimize controller for robot manipulator to track precisely trajectories optimized in the previous step.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 1992.08a
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• pp.146-149
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• 1992

The dynamic inelastic analysis is now often performed for the safe structural design against the seismic events or explosions. Several powerful methods of dynamic inelastic analysis such as direct intergration methods and modal superposition methods were developed with the development of computers during the last three decades. This type of analysis generally adopts the step-by-step time-integration procedure and gives a complete time history of the evolution of the structure.(omitted)