• The Journal of Korean Society for Radiation Therapy
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• v.18 no.2
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• pp.89-96
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• 2006

Purpose: To study effectiveness of heterogeneity correction of internal-body inhomogeneities and patient positioning immobilizers in dose calculation, using images obtained from CT-Simulator. Materials and Methods: A water phantom($250{\times}250{\times}250mm^3$) was fabricated and, to simulate various inhomogeneity, 1) bone 2) metal 3) contrast media 4) immobilization devices(Head holder/pillow/Vac-lok) were inserted in it. And then, CT scans were peformed. The CT-images were input to Radiation Treatment Planning System(RTPS) and the MUs, to give 100 cGy at 10 cm depth with isocentric standard setup(Field Size=$10{\times}10cm^2$, SAD=100 cm), were calculated for various energies(4, 6, 10 MV X-ray). The calculated MUs based on various CT-images of inhomogeneities were compared and analyzed. Results: Heterogeneity correction factors were compared for different materials. The correction factors were $2.7{\sim}5.3%$ for bone, $2.7{\sim}3.8%$ for metal materials, $0.9{\sim}2.3%$ for contrast media, $0.9{\sim}2.3%$ for Head-holder, $3.5{\sim}6.9%$ for Head holder+pillow, and $0.9{\sim}1.5%$ for Vac-lok. Conclusion: It is revealed that the heterogeneity correction factor calculated from internal-body inhomogeneities have various values and have no consistency. and with increasing number of beam ports, the differences can be reduced to under 1%, so, it can be disregarded. On the other hand, heterogeneity correction from immobilizers must be regarded enough to minimize inaccuracy of dose calculation.

• Proceedings of the KSRS Conference
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• 2005.10a
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• pp.589-592
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• 2005

Gravity characteristics and Moho undulations are investigated in the Korean peninsula by using satellite gravity data. According to the development of satellite geodesy, gravity potential models which have high accuracy and resolution were released. Using the EIGEN-CGOIC model based on low orbit satellite data such as CHAMP and GRACE, geoid and gravity anomaly were calculated by spherical harmonic analysis. The study area is located at $123^{\circ}\sim132^{\circ}E, 33^{\circ}\sim43^{\circ}$N including Korea. Free-air anomalies, which show the effect of terrain, have the values between $-37\sim724 mgal. After Bouguer correction, the range of simple Bouguer anomalies is $-221\sim246$ mgal. Complete Bouguer anomalies after terrain correction increase from continent to marine. This phenomenon is related rise of Moho discontinuity. The cut-frequency for extraction of Moho undulation was determined by power spectrum analysis, and then 3D inversion modeling was implemented. The mean, maximum, minimum, and standard deviation of Moho depth undulation are -26, -36, -8, and 4.9 krn, respectively.

• International Journal of Highway Engineering
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• v.20 no.3
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• pp.19-26
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• 2018

PURPOSES : The main purpose of this study is suggest of field bond strength evaluation method for more objective evaluation method through Evaluation of Bond Strength Properties with changing aspect ratio and temperature. METHODS : The evaluation is laboratory bond strength test. Using the core machine, the pull-off test method ; the bond strength test of interface layer the universal testing machine. RESULTS : As a result of the laboratory bond strength evaluation, it was verified that the bond strength by aspect ratio decreases linearly with increasing aspect ratio and the bond strength properties by temperature change existed at high and low temperature condition relative to odinary temperature condition. CONCLUSIONS : According to the results of laboratory bond strength evaluation, the field bond strength evaluation results suggest applying the proposed correction factor (0.8, 1.0, 1.4, 1.9) according to aspect ratio(0.5, 0.1, 1.5, 2.0), For more objective evaluation of the bond strength, it is analyzed that the evaluation value is within $6{\sim}32^{\circ}C$ and the result can be obtained within 5% of the coefficient of variation.

• Journal of radiological science and technology
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• v.22 no.2
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• pp.47-51
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• 1999

We calculated the energy distribution and the percentage depth-dose at 10 cm in a $10{\times}10\;cm^2$ with a photon beam at SSD of 100 cm by using a Monte Carlo Simulation. PDD is used as a beam-quality specifier for radiotherapy beams. It is better than the commonly used values of TPR or nominal accelerating potential. The presence of electron contamination affects the measurement of PDD, but can be removed by the use of a 0.1 cm lead filter. It reduces surface dose from contaminant electrons from the accelerator by more than 90% for radiotherapy beams. The filter performs best when it is placed immediately below the head. An electron-contamination correction factor is introduced to correct for electron contamination from the filter and air. It converts PDD which includes the electron contamination with the filter in place into PDD for the photons in the filtered beam. The correction factor can be used to determine stopping-power ratio. Calculations show that the values of water-to-air slopping power ratio in the unfiltered beam are related to PDD.

• Journal of Positioning, Navigation, and Timing
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• v.7 no.3
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• pp.165-173
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• 2018

Underwater vehicles use Inertial Navigation System (INS) with high-performance Inertial Measurement Unit (IMU) for high precision navigation. However, when underwater navigation is performed for a long time, the INS error gradually diverges, therefore, an integrated navigation method using auxiliary sensors is used to solve this problem. In terms of underwater vehicles, the vertical axis error is primarily compensated through Vertical Channel Damping (VCD) using a depth gauge, and an integrated navigation filter can be designed to perform horizontal axis error and sensor error correction using a speedometer such as Electromagnetic-Log (EM-Log). However, since EM-Log outputs the forward direction relative speed of the vehicle with respect to the sea and sea current, INS correction filter using this may cause a rather large error. Although it is possible to design proper filters if the exact model of the sea current is known, it is impossible to know the accurate model in reality. Therefore, this study proposes an INS/EM-Log integrated navigation filter with the function to estimate sea current using an Interacting Multiple Model (IMM) filters, and the performance of this filter is analyzed through a simulation performed in various environments.

• The Korean Journal of Nuclear Medicine
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• v.24 no.2
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• pp.260-266
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• 1990

Scintigraphic measurement of gastric emptying time has been reported to be influenced by the variation in depth of radionuclide within the stomach. In order to determine the effect of tissue attenuation in the measurement of gastric emptying time, 15 gastric emptying studies were performed with Tc-99m labeled egg sandwiches. Single anterior detector method overestimated the T1/2 by an average of 13% than geometric mean method and range of overestimation was wide (from -13% to 132%). Therefore, to evaluate the gastric empthying time accurately, methods of attenuation correction are needed.

• International Journal of Aerospace System Engineering
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• v.3 no.1
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• pp.10-16
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• 2016

A trigonometric Layerwise higher order shear deformation theory (TLHSDT) is developed and implemented for free vibration and buckling analysis of laminated composite and sandwich plates by analytical and finite element formulation. The present model assumes parabolic variation of out-plane stresses through the depth of the plate and also accomplish the zero transverse shear stresses over the surface of the plate. Thus a need of shear correction factor is obviated. The present zigzag model able to meet the transverse shear stress continuity and zigzag form of in-plane displacement continuity at the plate interfaces. Hence, botheration of shear correction coefficient is neglected. In the case of analytical method, the governing differential equation and boundary conditions are obtained from the principle of virtual work. For the finite element formulation, an efficient eight noded $C^0$ continuous isoparametric serendipity element is established and employed to examine the dynamic analysis. Like FSDT, the considered mathematical model possesses similar number of variables and which decides the present models computationally more effective. Several numerical predictions are carried out and results are compared with those of other existing numerical approaches.

• The Journal of Engineering Research
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• v.1 no.1
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• pp.49-57
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• 1997

In this paper, the follow-up works of Habermann's deadlock avoidance algorithm is investigated from the view of correction, efficiency and concurrency. Habermann's deadlock avoidance algorithm is briefly surveyed and in-depth discussion of follow-up algorithms modified and improved is presented. Then, further improvement of Kameda's algorithm will be discussed. His algorithm for testing deadlock-freedom in computer system converts the Habermann's model into a labeled bipartite graph so that the deadlock detection problem can be equivalent to finding complete matching for Mormon marriage problem. His algorithm has a running time of O($mn^1.5$) because Dinic's algorithm is used. The speed of above algorithm can be enhanced by employing a faster algorithm for finding a maximal matching. The wave method by Kazanov is used for.

• Nuclear Engineering and Technology
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• v.53 no.5
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• pp.1626-1633
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• 2021

In an industrial field, non-destructive testing (NDT) is commonly used to inspect industrial products. Among NDT methods using radiation sources, X-ray laminography has several advantages, such as high depth resolution and low computational costs. Moreover, an X-ray laminography system with stationary source array and compact detector is able to reduce mechanical motion artifacts and improve inspection efficiency. However, this system, called stationary inverse-geometry X-ray laminography (s-IGXL), causes truncation artifacts in reconstructed images due to limited fields-of-view (FOVs). In this study, we proposed a projection data correction (PDC) method to reduce the truncation artifacts arisen in s-IGXL images, and the performance of the proposed method was evaluated with the different number of focal spots in terms of quantitative accuracy. Comparing with conventional techniques, the PDC method showed superior performance in reducing truncation artifacts and improved the quantitative accuracy of s-IGXL images for all the number of focal spots. In conclusion, the PDC method can improve the accuracy of s-IGXL images and allow precise NDT measurements.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.5B
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• pp.551-555
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• 2006

In this study, new dispersion-correction terms are added to a leap-frog finite difference scheme for the linear shallow-water equations with the purpose of considering dispersion effects of the linear Boussinesq equations for propagation of tsunamis. The numerical model developed in this study is tested to the problem that the initial free surface displacement is a Gaussian hump over a constant water depth, and the predicted numerical results are compared with analytical solutions. The results of the present numerical model are accurate in comparison with those of existing models.