• Journal of the Korean Chemical Society
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• v.32 no.3
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• pp.227-232
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• 1988

A kinetic study was made to determine the mechanism of the aquation of $cis-[Co(en)_2(NH_3)Cl]^{2+}\;in\;Hg^{2+}$ aqueous solution. The progress of reaction was followed UV/vis-spectrophotometrically by a measurement of the absorbance at a specific wave length (530nm) of $cis-[Co(en)_2(NH_3)Cl]^{2+}$ as a function of time. The experimental results have shown that the reaction rate is dependent upon the concentration of $Hg^{2+}$ that act as a catalyst. And it was found that the overall reaction proceed with second order, first order with respect to Co(III) complex and $Hg^{2+}$. Activation parameters, ${\Delta}H^{\neq}\;and\;{\Delta}S^{\neq}$, were obtained as 12.9 kcal/mol and -19.3 e.u., respectively. We have proposed a plausible reaction mechanism which is consistent with the observed rate equation.

• Journal of Information Processing Systems
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• v.16 no.6
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• pp.1424-1436
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• 2020

Although huge progress has been made in current image segmentation work, there are still no efficient segmentation strategies for tree image which is taken from natural environment and contains complex background. To improve those problems, we propose a method for tree image segmentation combining adaptive mean shifting with image abstraction. Our approach perform better than others because it focuses mainly on the background of image and characteristics of the tree itself. First, we abstract the original tree image using bilateral filtering and image pyramid from multiple perspectives, which can reduce the influence of the background and tree canopy gaps on clustering. Spatial location and gray scale features are obtained by step detection and the insertion rule method, respectively. Bandwidths calculated by spatial location and gray scale features are then used to determine the size of the Gaussian kernel function and in the mean shift clustering. Furthermore, the flood fill method is employed to fill the results of clustering and highlight the region of interest. To prove the effectiveness of tree image abstractions on image clustering, we compared different abstraction levels and achieved the optimal clustering results. For our algorithm, the average segmentation accuracy (SA), over-segmentation rate (OR), and under-segmentation rate (UR) of the crown are 91.21%, 3.54%, and 9.85%, respectively. The average values of the trunk are 92.78%, 8.16%, and 7.93%, respectively. Comparing the results of our method experimentally with other popular tree image segmentation methods, our segmentation method get rid of human interaction and shows higher SA. Meanwhile, this work shows a promising application prospect on visual reconstruction and factors measurement of tree.

• Progress in Medical Physics
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• v.9 no.4
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• pp.259-266
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• 1998

To achieve the 2D dose distribution around the designed high dose rate Ir-192 source substitution for Co-60 brachytherapy source, we determined the exposure rate constant and tissue attenuation factors as a large depth as a 20 cm from source center. The exposure rate constant is used for apparent activity in designed source with self-absorption and encapsulation steel wall. The tissue dose delivered from the 4401 segments of 2.5 mm in a diameter and 2.5 mm height of disk-type source layer. In the experiments, the tissue attenuation factors include the tissue attenuation and multiple scattering in a medium surrounding the source. The fitted the polynomial regression with 4th order for the tissue attenuation factors are very closed to the experimental measurement data within ${\pm}$1% discrepancy. The Meisberger's constant showed the large uncertainty in large distance from source. The exposure rate constant 4.69 Rcm$^2$/mCi-hr was currently used for determination of apparent activity of source and air kerma strength was obtained 0.973 for tissue absorbed dose from the energy spectrum of Ir-192 source. In our experiments with designed high dose rate brachytherapy source, the apparent activity of Ir-192 source was delivered from the 54.6 % of actual physical source activity through the self-absorption and encapsulation wall attenuations. This paper provides the 2-dimensional dose tabulation from unit apparent activity in a water medium for dose planning includes the multiple scattering, source anisotropy effect and geometric factors.

• Progress in Medical Physics
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• v.27 no.1
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• pp.25-30
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• 2016

The dosimetric characteristics were experimentally evaluated for electron beams from the prototype linac developed for radiotherapy units. This paper focuses on the electron beam output and energy variations as a function of electron gun heater current. The electron energy was derived from its mean and most probable energies measured by film dosimetry. The electron beam output at the maximum electron energy was measured with the plane parallel ionization chamber in water using TRS-398 dosimetry protocol. The mean energy and the most probable energy of the electron beam were 6.54~3.31 MeV and 5.94~2.80 MeV at electron gun current of 2.02~2.50 A respectively. The output dose rate for an electron beam of mean energy 6.54 MeV was 5.41 Gy/min ${\pm}1.5%$ at the reference depth in water.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.2
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• pp.619-626
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• 2020

The development of new antifreeze mixtures containing non-amine-type corrosion inhibitors, which considers environmental protection, has become a major issue. In this study, four non-amine-type corrosion inhibitors were synthesized and used to produce five kinds of new antifreeze for automobiles to evaluate the rate of copper corrosion. The effects were evaluated by the weight change, surface observation, roughness measurement, and measurement of copper elution in the solution. The amount of copper eluted measured by ICP from Sample 4 was small, and the elution rate was prolonged. Sample 4 showed the best anti-corrosion performance owing to a corrosion suppression effect by passivating copper because the metal surface was smooth after the test, and the corrosion product layer was formed evenly on the surface as small local corrosion was observed. The major corrosion inhibitor added to Sample 4 was 1-aminomethyl(N',N'-di(2-hydroxyethyl)benzotrazole, which contained a certain amount in Sample 5 to show relatively high local corrosion but passivation in progress. Therefore, among the four corrosion inhibitors, 1-aminomethyl(N',N'-di(2-hydroxyethyl)benzotrazole had the highest corrosion inhibitory effect. This corrosion inhibitor prevents corrosion by promoting the passivation of copper on the antifreeze.

• Progress in Medical Physics
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• v.8 no.1
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• pp.25-29
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• 1997

Ir-192 source activity for high dose rate brachytherapy is measured using Farmertype ionization chamber. The source-to-chamber distance is 10 cm and the measured charge unit is converted to activity unit. The measured values are compared to the values provided from vendor. Because of time dependency of Ir-192 source activity, the activities are regularly checked and compared to calculated values. As the accuracy of Ir-192 source activity is depend on the mechanical measurement setup, we estimated the precision of remote controlled source dwell position using home-made device and film scanner. The difference between measured and predicted dwell position is within 1 mm. As a result, the errors of source activity are 0.7${\pm}$1.5 ％ for measured and vendor-provided values and 0.l${\pm}$1.2％ for measured and time-dependent calculated vlaues. In conclusion, our measured activity has been comparable to the values provided from vendor and our brachytherapy unit has been very accurate until now. Regular quality control of brachytherapy is essential for successful treatment which depends on the accuracy of source position and activity.

• Progress in Medical Physics
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• v.26 no.1
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• pp.1-5
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• 2015

The C-band compact linear accelerator (linac) is being developed at Dongnam Institute of radiological & Medical Sciences (DIRAMS) for medical and industrial applications. This paper was focused on the output measurement of the electron beam generated from the prototype electron linac. The dose rate was measured in unit of cGy/min per unit pulse frequency according to the IAEA TRS-398 protocol. Exradin-A10 Markus type plane parallel chamber used for the measurement was calibrated in terms of dose to water at the reference depth in water. The beam quality index ($R_{50}$) was determined by the radiochromic film with a solid water phantom approximately due to low energy electrons. As a result, the determined electron beam output was $17.0cGy/(min{\cdot}Hz$. The results were used to monitor the accelerator performance during the development procedure.

• Progress in Medical Physics
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• v.24 no.1
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• pp.41-47
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• 2013

We evaluated the influence of volume effect on the measurement of IMRT dose distribution by comparing a 2D-array ion chamber and other dosimeters. Matrix phantom which is a 2D-array ion chamber having volume effect was compared with beam image system and film for the measurement of dose distribution. Five intensity-modulated radiation therapy plans were created using five fields in thevirtual phantom. The measured dose distribution was compared with the calculated one by radiation treatment planning system and analysis program. We evaluated the conformity of dose distribution by calculating correlation coefficients and gamma values. The highest error rate of 1.3% was associated with matrix phantom in which volume effect in small field sizes was substantial.

• Progress in Medical Physics
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• v.15 no.2
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• pp.105-111
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• 2004

The parallel plate detector with dielectric film for dosimetry was designed to measure detection characteristic of 6 MV X-ray with medical linear accelerator. PTFE film was inserted into FEP films that are made by two one-side metal coated materials for ion source. The thicknesses of PTFE dielectric film was 100 ${\mu}{\textrm}{m}$ and the thickness of FEP dielectric film was 100 ${\mu}{\textrm}{m}$, respectively. This detector was fixed by two acrylic plate for physical hardness ad geometrical consistency. The geometrical condition for measurement with parallel-plate for detector was below; SSD=100 cm and the 5 cm depth between detector and phantom surface The major parameter of detector characteristics such as zero drift current, leakage current, charge response by applied voltage, reproducibility, linearity, TMR measurement, dose rate effect were measured. The zero drift currents are 8.3 pA and leakage currents are 10 pA. The charge response of applied voltage is showing linearity in 414 voltage. The measurement deviation of reproducibility in this detector is within 1% for dose and the linearity of applied dose shows in this detector. The TMR curves in phantom between this parallel plate detector and reference detector are matched within 3% deviation from maximum dose depth to 7.5 cm depth. It is considered that this dosimetric system is satisfactory for the purpose of the constancy check of the 6 MV x-ray from medical linear accelerator.

• Progress in Medical Physics
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• v.30 no.4
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• pp.128-138
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• 2019

Purpose: Segmental analysis of volumetric modulated arc therapy (VMAT) is not clinically used for compositional error source evaluation. Instead, dose verification is routinely used for plan-specific quality assurance (QA). While this approach identifies the resultant error, it does not specify which machine parameter was responsible for the error. In this research study, we adopted an approach for the segmental analysis of VMAT as a part of machine QA of linear accelerator (LINAC). Methods: Two portal dose QA plans were generated for VMAT QA: a) for full arc and b) for the arc, which was segmented in 12 subsegments. We investigated the multileaf collimator (MLC) position and dosimetric accuracy in the full and segmented arc delivery schemes. A MATLAB program was used to calculate the MLC position error from the data in the dynalog file. The Gamma passing rate (GPR) and the measured to planned dose difference (DD) in each pixel of the electronic portal imaging device was the measurement for dosimetric accuracy. The eclipse treatment planning system and a MATLAB program were used to calculate the dosimetric accuracy. Results: The maximum root-mean-square error of the MLC positions were <1 mm. The GPR was within the range of 98%-99.7% and was similar in both types of VMAT delivery. In general, the DD was <5 calibration units in both full arcs. A similar DD distribution was found for continuous arc and segmented arcs sums. Exceedingly high DD were not observed in any of the arc segment delivery schemes. The LINAC performance was acceptable regarding the execution of the VMAT QA plan. Conclusions: The segmental analysis proposed in this study is expected to be useful for the prediction of the delivery of the VMAT in relation to the gantry angle. We thus recommend the use of segmental analysis of VMAT as part of the regular QA.