• Korean Journal of Agricultural and Forest Meteorology
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• v.13 no.4
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• pp.176-184
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• 2011

Cold air on sloping surfaces flows down to the valley bottom in mountainous terrain at calm and clear nights. Based on the assumption that the cold air flow may be the same as the water flow, current models estimate temperature drop by regarding the cold air accumulation at a given location as the water-like free drainage. At a closed catchment whose outlet is blocked by man-made obstacles such as banks and roads, however, the water-like free drainage assumption is no longer valid because the cold air accumulates from the bottom first. We developed an empirical model to estimate quantitatively the effect of cold pool on nocturnal temperature in a closed catchment. In our model, a closed catchment is treated like a "vessel", and a digital elevation model (DEM) was used to calculate the maximum capacity of the cold pool formed in a closed catchment. We introduce a topographical variable named "shape factor", which is the ratio of the cold air accumulation potential across the whole catchment area to the maximum capacity of the cold pool to describe the relative size of temperature drop at a wider range of catchment shapes. The shape factor is then used to simulate the density profile of cold pool formed in a given catchment based on a hypsometric equation. The cold lake module was incorporated with the existing model (i.e., Chung et al., 2006), generating a new model and predicting distribution of minimum temperature over closed catchments. We applied this model to Akyang valley (i.e., a typical closed catchment of 53 $km^2$ area) in the southern skirt of Mt. Jiri National Park where 12 automated weather stations (AWS) are operational. The performance of the model was evaluated based on the feasibility of delineating the temperature pattern accurately at cold pool forming at night. Overall, the model's ability of simulating the spatial pattern of lower temperature were improved especially at the valley bottom, showing a similar pattern of the estimated temperature with that of thermal images obtained across the valley at dawn (0520 to 0600 local standard time) of 17 May 2011. Error in temperature estimation, calculated with the root mean square error using the 10 low-lying AWSs, was substantially decreased from $1.30^{\circ}C$ with the existing model to $0.71^{\circ}C$ with the new model. These results suggest the feasibility of the new method in predicting the site-specific freeze and frost warning at a closed catchment.

• Radiation Oncology Journal
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• v.16 no.2
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• pp.185-194
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• 1998

Purpose : With the development of stereotactic immobilization systems capable of reliable serial repositioning, fractionated stereotactic radiation therapy (FSRT) offers the Potential for an improved treatment outcome by excellent dose delivery, and dose distribution characteristics with the favorable radiobiological properties of fractionated irradiation. We describe our initial experience using FSRT for the treatment of intracranial benign tumor. Materials and Methods : Between August 1995 and December 1996. 15 patients(7 males and 8 females aged 6-70 years) were treated with FSRT. The patients had the following diagnosis pituitary adenoma(10) including one patient who previously had received radiotherapy, craniopharyngioma (2), acoustic neurinoma (1), meningioma (2). Using the Gill-Thomas-Cosman relocatable head frame and multiple non-coplanar therapy, the daily dose of 2Gy was irradiated at 90% to 100% isodose surface of the isocenter The collimator sizes ranged from 26mm to 70mm. Results : In all patients except one follow-up lost, disease was well-controlled. Acute complication was negligible and no patient experienced cranial nerve neuropathies and radiation necrosis. In overall patient setup with scalp measurements, reproducibility was found to have mean of $1.1{\pm}0.6mm$ from the baseline reading. Conclusion : Relocatable stereotactic system for FSRT is highly reproducible and comfortable. Although the follow-up period was relatively short. FSRT is considered to be a safe and effective radiation technique as the treatment of intracranial tumor. But the fractionation schedule(fraction size, overall treatment time and total dose) still remains to be solved by further clinical trials.

• The Korean Journal of Nuclear Medicine
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• v.32 no.4
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• pp.382-390
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• 1998

Purpose: The purpose of this study was to evaluate the accuracy of radioactivity quantitation in Tc-99m SPECT by using combined scatter and attenuation correction. Materials and Methods: A cylindrical phantom which simulates tumors (T) and normal tissue (B) was filled with varying activity ratios of Tc-99m. We acquired emission scans of the phantom using a three-headed SPECT system (Trionix, Inc.) with two energy windows (photopeak window: $126{\sim}154keV$ and scatter window: $101{\sim}123keV$). We performed the scatter correction with dual-energy window subtraction method (k=0.4) and Chang attenuation correction. Three sets of SPECT images were reconstructed using combined scatter and attenuation correction (SC+AC), attenuation correction (AC) and without any correction (NONE). We compared T/B ratio, image contrast [(T-B)/(T+B)] and absolute radioactivity with true values. Results: SC+AC images had the highest mean values of T/B ratios. Image contrast was 0.92 in SC+AC, which was close to the true value of 1, and higher than AC (0.77) or NONE (0.80). Errors of true activity by SPECT images ranged from 1 to 11% for SC+AC, $22{\sim}47%$ for AC, and $2{\sim}16%$ for NONE in a phantom which was located 2.4cm from the phantom surface. In a phantom located 10.0cm from the surface, SC+AC underestimated by 24%, NONE 40%. However, AC overestimated by 10%. Conclusion: We conclude that accurate SPECT activity quantitation of Tc-99m distribution can be achieved by dual window scatter correction combind with attenuation correction.

• Nuclear Medicine and Molecular Imaging
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• v.43 no.5
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• pp.459-467
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• 2009

Purpose: The maximum likelihood-expectation maximization (ML-EM) is the statistical reconstruction algorithm derived from probabilistic model of the emission and detection processes. Although the ML-EM has many advantages in accuracy and utility, the use of the ML-EM is limited due to the computational burden of iterating processing on a CPU (central processing unit). In this study, we developed a parallel computing technique on GPU (graphic processing unit) for ML-EM algorithm. Materials and Methods: Using Geforce 9800 GTX+ graphic card and CUDA (compute unified device architecture) the projection and backprojection in ML-EM algorithm were parallelized by NVIDIA's technology. The time delay on computations for projection, errors between measured and estimated data and backprojection in an iteration were measured. Total time included the latency in data transmission between RAM and GPU memory. Results: The total computation time of the CPU- and GPU-based ML-EM with 32 iterations were 3.83 and 0.26 see, respectively. In this case, the computing speed was improved about 15 times on GPU. When the number of iterations increased into 1024, the CPU- and GPU-based computing took totally 18 min and 8 see, respectively. The improvement was about 135 times and was caused by delay on CPU-based computing after certain iterations. On the other hand, the GPU-based computation provided very small variation on time delay per iteration due to use of shared memory. Conclusion: The GPU-based parallel computation for ML-EM improved significantly the computing speed and stability. The developed GPU-based ML-EM algorithm could be easily modified for some other imaging geometries.

• Journal of The Korean Society of Grassland and Forage Science
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• v.19 no.3
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• pp.265-272
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• 1999

In this study in order to know the behavior of mineral nutrients from forage plant to soil in a grassland ecosystem, the leaching of minerals (K, Mg, Ca, N and P) from air-dried (dead) plant body was investigated by putting orchardgrass (Dactylis glomerata L.) hay on meadow during a month with seasonal changes. The results obtained were as follows; 1) The K content of the forage, not stable during the experimental seasons, tended to decrease in the summer of 1986, while the Mg and Ca contents increased in the summer. The reason might be a different response (solubility or leaching liability) of the monovalent mineral (K) and divalent ones (Mg and Ca) in the forage to rainfall. 2) The percentage of P to the initial amount in the forage showed larger decrease in a rainy period (Feb.~Mar., 1986) and during the rainy summer (May to July). The P component of the forage might be easily leached with water. 3) The percentage of the four minerals (Ca, N, Mg, K) remained the least in the period of (Jun.~Jul., 1986), 4) Though the percentage of remained Mg and N of the forage varied very similarly, the percentage of remained N was higher than that of Mg during periods before summer (January to May), while after the period the ratio of the Mg seemed to be higher than that of the N (June to December), 5) During the periods until (May~Jun., 1986) the percentage of remained K and P of the forage varied in very similar pattern, and the order of remained mineral was as follows; $Ca>N{\geq}Mg>P=K$. But from the period of (Jun-Jul) the ratio of P remained in the forage increased nearly up to the ratio of N, and the order was as follows; $Ca>Mg{\geq}N{\geq}P>K$.

• Progress in Medical Physics
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• v.14 no.2
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• pp.90-98
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• 2003

Purpose : A new virtual simulation technique for craniospinal irradiation (CSI) that uses a CT-simulator was developed to improve the accuracy of field and shielding placement as well as patient positioning. Materials and Methods : A CT simulator (CT-SIM) and a 3-D conformal radiation treatment planning system (3D-CRT) were used to develop CSI. The head and neck were immobilized with a thermoplastic mask while the rest of the body was immobilized with a Vac-Loc. A volumetric image was then obtained with the CT simulator. In order to improve the reproducibility of the setup, datum lines and points were marked on the head and body. Virtual fluoroscopy was performed with the removal of visual obstacles, such as the treatment table or immobilization devices. After virtual simulation, the treatment isocenters of each field were marked on the body and on the immobilization devices at the conventional simulation room. Each treatment fields was confirmed by comparing the fluoroscopy images with the digitally reconstructed radiography (DRR) and digitally composited radiography (DCR) images from virtual simulation. Port verification films from the first treatment were also compared with the DRR/DCR images for geometric verification. Results : We successfully performed virtual simulations on 11 CSI patients by CT-SIM. It took less than 20 minutes to affix the immobilization devices and to obtain the volumetric images of the entire body. In the absence of the patient, virtual simulation of all fields took 20 min. The DRRs were in agreement with simulation films to within 5 mm. This not only reducee inconveniences to the patients, but also eliminated position-shift variables attendant during the long conventional simulation process. In addition, by obtaining CT volumetric image, critical organs, such as the eyes and the spinal cord, were better defined, and the accuracy of the port designs and shielding was improved. Differences between the DRRs and the portal films were less than 3 m in the vertebral contour. Conclusion : Our analysis showed that CT simulation of craniospinal fields was accurate. In addition, CT simulation reduced the duration of the patient's immobility. During the planning process. This technique can improve accuracy in field placement and shielding by using three-dimensional CT-aided localization of critical and target structures. Overall, it has improved staff efficiency and resource utilization by standard protocol for craniospinal irradiation.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.32 no.2 s.57
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• pp.105-110
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• 2006

This study was to describe the differences in efficacy and effect of herbal extracts by the part and solvent extraction from the medical plants used as materials of oriental herbs cosmetics. And, this study was to apply to the test method of efficacy and effect related to the antioxidation as herbal extracts, complex of actual ingredient, not existing analytical methods of single ingredient. After screening the medical plants with the antioxidative activity primarily and selecting 11 sorts of medical plants to be used by the part in the literature, this study was to confirm the differences through the well-known test methods like DPPH radical scavenging activity test and hydroxyl radical scavenging activity test. For examples, in case of Trachelospermum asiaticum, compared with the aerial part and fruit, the value of DPPH radical scavenging activity test had $25.2 {\pm} 0.2$ and $62.4 {\pm}1.6$ each. It has shown that the value of fruit had 2.4 times higher effect than the one of aerial part. In case of hydroxyl scavenging activity test, it was effective in the fruit, but it has shown that there was no effect on the aerial part. It showed the same phenomena in some other plants. From the result above, this researcher could understand that it needed to consider extracting the medical plants or plants with the active principle by the part. Also, this study was to confirm the differences in effect according to the solvent as it changed the solvent extraction after selecting a plant (Lithospermum erythrorhizon) widely used for medicine and dye. As a result of measuring the actual value of superoxide scavenging activity test, this study was to consider that there were differences by the part or solvent extraction in extracting and using the medical plants as it has shown that the effect differences produced $10{\sim}80%$ according to the solvent. When it was applied to the products, this study has shown that it needed to decrease the possible errors.

• Polymer(Korea)
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• v.30 no.6
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• pp.498-504
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• 2006

A suspension polymerization of styrene In aqueous phase was employed to study if polystyrene particles ranging from 1 to $20{\mu}m$ can be produced. Hydrophobic silica was selected as a stabilizer and azo-bisisobutyronitrile (AIBN) as an initiator. Polymerization reaction was carried out at a selected temperature in the range of $65{\sim}95^{\circ}C$. Stabilizer concentration was varied from 0.17 to 3.33 wt% compared to the water while the concentration of the initiator was raised from 0.13 to 6.0 wt% compared to the monomer. Dispersion of hydrophobic silica into the water phase was achieved by precise control of pH. Optimum dispersion of silica was obtained at pH 10. Average particle diameter decreased with increasing amounts of stabilizer concentration initially, exhibiting the minimum average diameter at 1.67 wt% of stabilizer concentration, after which it started to Increase. It is speculated that an excessive presence of stabilizer encouraged a secondary reaction in the reaction medium, which led to particle agglomeration, and as a result an increase in average particle diameter. Molecular weight was found to be independent of stabilizer concentration between 0.13 and 1.00 wt% whereas, it increased when stabilizer concentration exceeded 1.67 wt%. Variation of molecular weight was probably caused by the reduced activity and efficiency of initiator due to the high concentration of silica, and the secondary reaction in the reaction medium, as well. An increase in the Initiator concentration and/or reaction temperature resulted in an increase in both reaction rate and particle diameter. Consequently, we have confirmed that spherical polystyrene particles with $1{\sim}20{\mu}m$ in diameter can be prepared by careful selection of the concentration of stabilizer, initiator, pH and reaction temperature.

• Korean Journal of Agricultural and Forest Meteorology
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• v.18 no.1
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• pp.1-15
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• 2016

Annual litterfall production and leaf area index (LAI, $m^2/m^2$) were estimated using litter traps in Gwangneung, Mt. Taewha and Mt. Gariwang. Annual total litter fall production including branch, bark, others was the highest in Gwangneung($7497.3{\pm}326.5kg/ha/yr$), which had the highest basal area at late successional stage, and followed by Mt. Taewha($5929.1{\pm}225.8kg/ha/yr$) and Mt. Gariwang($3,210.1{\pm}220.1kg/ha/yr$). Mt. Gariwang had the lowest litterfall production due to high elevation and short growing season even with the higher stand density and basal area than Mt. Taewha. Similarly, LAI, which was calculated by multiplying the mass of leaf litter with specific leaf area, was the highest in Gwangneung($5.99{\pm}0.69$) and followed by Mt. Taewha($5.20{\pm}0.24$) and Mt. Gariwang($4.06{\pm}0.42$) and the upper canopy species had the highest leaf area index in every sites (Gwangneung : 4.72, Mt. Taewha : 3.08, Mt. Gariwang : 2.19). However, species specific LAI estimation based on the relationship between basal area and leaf area was limited due to upper canopy species non-proportionality of basal area with LAI. In addition, the comparison between direct and indirect LAI measurement showed the importance of canopy clumping, especially at high density. Our study emphasized the necessity of direct LAI measurement using litter fall traps especially at temperate deciduous forest with diverse species.

• Journal of the Korea Concrete Institute
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• v.23 no.6
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• pp.711-722
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• 2011

Beam-column gravity or Intermediate Moment frames subjected to unexpected large displacements are vulnerable when no seismic details are provided, which is typical. Conversely, economic efficiency of those frames is decreased if unnecessary special detailing is applied as the beam and column size becomes quite large and steel congestion is caused by joint transverse reinforcement in beam-column connections. Moderate seismic design is used in Korea for beam-column connections of buildings with structural walls, which are to be destroyed when the unexpected large earthquake occurs. Nonetheless, performance of such beamcolumn connections may be substantially improved by the addition of steel fibers. This study was conducted to investigate the effect of steel fibers in reinforced concrete exterior beam-column connections and possibility for the replacement of some joint transverse reinforcement. Ten half-scale beam-column connections with non-seismic details were tested under cyclic loads with two cycles at each drift up to 19 cycles. Main test parameters used were the volume ratio of steel fibers (0%, 1%, 1.5%) and joint transverse reinforcement amount. The test results show that maximum capacity, energy dissipation capacity, shear strength and bond condition are improved with the application of steel fibers to substitute transverse reinforcement of beam-column connections. Furthermore, several shear strength equations for exterior connections were examined, including the proposed equation for steel fiber-reinforced concrete exterior connections with non-seismic details.