• Advances in materials Research
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• v.12 no.4
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• pp.309-330
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• 2023

The humid thermal vibration characteristics of a nonhomogeneous thermopiezoelectric nonlocal plate of polygonal shape are addressed in the purview of generalized nonlocal thermoelasticity. The plate is initially stressed, and the three-dimensional linear elasticity equations are taken to form motion equations. The problem is solved using the Fourier expansion collocation method along the irregular boundary conditions. The numerical results of physical variables have been discussed for the triangle, square, pentagon, and hexagon shapes of the plates and are given as dispersion curves. The amplitude of non-dimensional frequencies is tabulated for the longitudinal and flexural symmetric modes of the thermopiezoelectric plate via moisture and thermal constants. Also, a comparison of numerical results is made with existing literature, and good agreement is reached.

• Structural Engineering and Mechanics
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• v.53 no.5
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• pp.981-995
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• 2015

This paper presents a finite element procedure for dynamic analysis of non-uniform Timoshenko beams made of axially Functionally Graded Material (FGM) under multiple moving point loads. The material properties are assumed to vary continuously in the longitudinal direction according to a predefined power law equation. A beam element, taking the effects of shear deformation and cross-sectional variation into account, is formulated by using exact polynomials derived from the governing differential equations of a uniform homogenous Timoshenko beam element. The dynamic responses of the beams are computed by using the implicit Newmark method. The numerical results show that the dynamic characteristics of the beams are greatly influenced by the number of moving point loads. The effects of the distance between the loads, material non-homogeneity, section profiles as well as aspect ratio on the dynamic responses of the beams are also investigated in detail and highlighted.

• Smart Structures and Systems
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• v.9 no.5
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• pp.427-439
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• 2012

The present paper deals with the analytical solution of a functionally graded piezoelectric (FGP) cylinder in the magnetic field under mechanical, thermal and electrical loads. All mechanical, thermal and electrical properties except Poisson ratio can be varied continuously and gradually along the thickness direction of the cylinder based on a power function. The cylinder is assumed to be axisymmetric. Steady state heat transfer equation is solved by considering the appropriate boundary conditions. Using Maxwell electro dynamic equation and assumed magnetic field along the axis of the cylinder, Lorentz's force due to magnetic field is evaluated for non homogenous state. This force can be employed as a body force in the equilibrium equation. Equilibrium and Maxwell equations are two fundamental equations for analysis of the problem. Comprehensive solution of Maxwell equation is considered in the present paper for general states of non homogeneity. Solution of governing equations may be obtained using solution of the characteristic equation of the system. Achieved results indicate that with increasing the non homogenous index, different mechanical and electrical components present different behaviors along the thickness direction. FGP can control the distribution of the mechanical and electrical components in various structures with good precision. For intelligent properties of functionally graded piezoelectric materials, these materials can be used as an actuator, sensor or a component of piezo motor in electromechanical systems.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.37 no.5
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• pp.351-357
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• 2019

UAV (Unmanned Aerial Vehicle) images can be exploited for rapid forest fire damage assessment by virtue of UAV systems' advantages. In 2019, catastrophic forest fire occurred in Goseong and Sokcho, Korea and burned 1,757 hectares of forests. We visited the town in Goseong where suffered the most severe damage and conducted UAV flights for forest fire damage assessment. In this study, economic and rapid damage assessment method for forest fire has been proposed using UAV systems equipped with only a RGB sensor. First, forest masking was performed using automatic elevation thresholding to extract forest area. Then ExG (Excess Green) vegetation index which can be calculated without near-infrared band was adopted to extract damaged forests. In addition, entropy filtering was applied to ExG for better differentiation between damaged and non-damaged forest. We could confirm that the proposed forest masking can screen out non-forest land covers such as bare soil, agriculture lands, and artificial objects. In addition, entropy filtering enhanced the ExG homogeneity difference between damaged and non-damaged forests. The automatically detected damaged forests of the proposed method showed high accuracy of 87%.

• Progress in Superconductivity and Cryogenics
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• v.12 no.2
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• pp.9-12
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• 2010

A lamination system using reflow soldering was developed to enhance the mechanical properties of high temperature superconductor (HTS) tape. The laminated coated conductor tape was fabricated using the continuous lamination process. The mean, maximum, and minimum tensile loads in a T-peel test of the laminated coated conductor were 9.9 N, 12.5 N, and 7.6 N, respectively. The critical current ($I_c$) distributions of the non-laminated and laminated coated conductor were compared using anon-contact Hall probe method. The transport $I_c$ nearly matched the non-contact $I_c$; however, some degraded Ic regions were found on the length of 800 cm of laminated coated conductor. We confirmed that the cause of the partially degraded $I_c$ was due to an increase in line tension by (1) solidification induced by a change of composition that usually occurs in molten brass (Cu, Zn) in solder, or (2) non-homogeneity of the thickness of the coated conductor or metal tapes. We suggest that reflow soldering is a promising method for reinforced HTS tape if the controlling solder thickness and lamination guide are modified.

• The Journal of Korean Society for Radiation Therapy
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• v.29 no.2
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• pp.9-17
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• 2017

Purpose: The tissue description and electron density indicated by the Computed Tomography(CT) number (also known as Hounsfield Unit) in radiotherapy are important in ensuring the accuracy of CT-based computerized radiotherapy planning. The internal metal implants, however, not only reduce the accuracy of CT number but also introduce uncertainty into tissue description, leading to development of many clinical algorithms for reducing metal artifacts. The purpose of this study was, therefore, to investigate the accuracy and the clinical applicability by analyzing date from SMART MAR (GE) used in our institution. Methode: and material: For assessment of images, the original images were obtained after forming ROIs with identical volumes by using CIRS ED phantom and inserting rods of six tissues and then non-SMART MAR and SMART MAR images were obtained and compared in terms of CT number and SD value. For determination of the difference in dose by the changes in CT number due to metal artifacts, the original images were obtained by forming PTV at two sites of CIRS ED phantom CT images with Computerized Treatment Planning (CTP system), the identical treatment plans were established for non-SMART MAR and SMART MAR images by obtaining unilateral and bilateral titanium insertion images, and mean doses, Homogeneity Index(HI), and Conformity Index(CI) for both PTVs were compared. The absorbed doses at both sites were measured by calculating the dose conversion constant (cCy/nC) from ylinder acrylic phantom, 0.125cc ionchamber, and electrometer and obtaining non-SMART MAR and SMART MAR images from images resulting from insertions of unilateral and bilateral titanium rods, and compared with point doses from CTP. Result: The results of image assessment showed that the CT number of SMART MAR images compared to those of non-SMART MAR images were more close to those of original images, and the SD decreased more in SMART compared to non-SMART ones. The results of dose determinations showed that the mean doses, HI and CI of non-SMART MAR images compared to those of SMART MAR images were more close to those of original images, however the differences did not reach statistical significance. The results of absorbed dose measurement showed that the difference between actual absorbed dose and point dose on CTP in absorbed dose were 2.69 and 3.63 % in non-SMRT MAR images, however decreased to 0.56 and 0.68 %, respectively in SMART MAR images. Conclusion: The application of SMART MAR in CT images from patients with metal implants improved quality of images, being demonstrated by improvement in accuracy of CT number and decrease in SD, therefore it is considered that this method is useful in dose calculation and forming contour between tumor and normal tissues.

• The Journal of Korean Society for Radiation Therapy
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• v.30 no.1_2
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• pp.9-16
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• 2018

Purpose : Brain Stereotactic Radiosurgery can treat non-invasive diseases with high rates of complications due to surgical operations. However, brain stereotactic radiosurgery may be accompanied by radiation induced side effects such as fractionation radiation therapy because it uses radiation. The effects of Coplanar Volumetric Modulated Arc Therapy(C-VMAT) and Non-Coplanar Volumetric Modulated Arc Therapy(NC-VMAT) on surrounding normal tissues were analyzed in order to reduce the side effects caused fractionation radiation therapy such as head and neck. But, brain stereotactic radiosurgery these contents were not analyzed. In this study, we evaluated the usefulness of NC-VMAT by comparing and analyzing C-VMAT and NC-VMAT in patients who underwent brain stereotactic radiosurgery. Methods and materials : With C-VMAT and NC-VMAT, 13 treatment plans for brain stereotactic radiosurgery were established. The Planning Target Volume ranged from a minimum of 0.78 cc to a maximum of 12.26 cc, Prescription doses were prescribed between 15 and 24 Gy. Treatment machine was TrueBeam STx (Varian Medical Systems, USA). The energy used in the treatment plan was 6 MV Flattening Filter Free (6FFF) X-ray. The C-VMAT treatment plan used a half 2 arc or full 2 arc treatment plan, and the NC-VMAT treatment plan used 3 to 7 Arc 40 to 190 degrees. The angle of the couch was planned to be 3-7 angles. Results : The mean value of the maximum dose was $105.1{\pm}1.37%$ in C-VMAT and $105.8{\pm}1.71%$ in NC-VMAT. Conformity index of C-VMAT was $1.08{\pm}0.08$ and homogeneity index was $1.03{\pm}0.01$. Conformity index of NC-VMAT was $1.17{\pm}0.1$ and homogeneity index was $1.04{\pm}0.01$. $V_2$, $V_8$, $V_{12}$, $V_{18}$, $V_{24}$ of the brain were $176{\pm}149.36cc$, $31.50{\pm}25.03cc$, $16.53{\pm}12.63cc$, $8.60{\pm}6.87cc$ and $4.03{\pm}3.43cc$ in the C-VMAT and $135.55{\pm}115.93cc$, $24.34{\pm}17.68cc$, $14.74{\pm}10.97cc$, $8.55{\pm}6.79cc$, $4.23{\pm}3.48cc$. Conclusions : The maximum dose, conformity index, and homogeneity index showed no significant difference between C-VMAT and NC-VMAT. $V_2$ to $V_{18}$ of the brain showed a difference of at least 0.5 % to 48 %. $V_{19}$ to $V_{24}$ of the brain showed a difference of at least 0.4 % to 4.8 %. When we compare the mean value of $V_{12}$ that Radione-crosis begins to generate, NC-VMAT has about 12.2 % less amount than C-VMAT. These results suggest that if NC-VMAT is used, the volume of $V_2$ to $V_{18}$ can be reduced, which can reduce Radionecrosis.

• Investigative Magnetic Resonance Imaging
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• v.24 no.3
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• pp.95-122
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• 2020

In this article, we evaluated the performance of radiofrequency (RF) coils in terms of the signal-to-noise ratio (S/N) and homogeneity of magnetic resonance images when used for ultrahigh-frequency (UHF) 7T magnetic resonance imaging (MRI). High-quality MRI can be obtained when these two basic requirements are met. However, because of the dielectric effect, 7T magnetic resonance imaging still produces essentially a non-uniform magnetic flux (|B₁|) density distribution. In general, heterogeneous and homogeneous RF coils may be designed using electromagnetic (EM) modeling. Heterogeneous coils, which are surface coils, are used in consideration of scalability in the |B₁| region with a high S/N as multichannel loop coils rather than selecting a single loop. Loop coils are considered state of the art for their simplicity yet effective |B₁|-field distribution and intensity. In addition, combining multiple loop coils allows phase arrays (PA). PA coils have gained great interest for use in receiving signals because of parallel imaging (PI) techniques, such as sensitivity encoding (SENSE) and generalized autocalibrating partial parallel acquisition (GRAPPA), which drastically reduce the acquisition time. With the introduction of a parallel transmit coil (pTx) system, a form of transceiver loop arrays has also been proposed. In this article, we discussed the applications and proposed designs of loop coils. RF homogeneous coils for volume imaging include Alderman-Grant resonators, birdcage coils, saddle coils, traveling wave coils, transmission line arrays, composite right-/left-handed arrays, and fusion coils. In this article, we also discussed the basic operation, design, and applications of these coils.

• Tunnel and Underground Space
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• v.18 no.3
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• pp.185-193
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• 2008

We have carried out Pearson-type chi-square tests on the orientation data of joints from different depths in order to estimate the homogeneity of joint orientations obtained from a borehole. The orientation data of joints were collected from two non-foliated massive rocks of granitic gneisses in South Korea since orientations of joints in folded metamorphic rocks, for example, are controlled by foliation and also changes as the orientations of foliation change by folding. Borehole images were used for the analysis of the orientations of individual joints. The orientation data were subdivided into the upper level data and lower level data. The data from these two levels are plotted on the patch net consisting of 21 orientation patches. Then, the two patterns on the patch net were analyzed using a contingency table. From the chi-square test on the data collected from two sites, we found that some data sets show statistically meaningful differences in orientations of joints. Since joints are one of the important parameters in determining the physical properties of rock masses, in situ investigation of joints are desirable in the geotechnical investigation and also in design of subsurface structures (e.g. tunnels and underground storages).

• Animal cells and systems
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• v.16 no.2
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• pp.145-153
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• 2012

The pear psylla, $Cacopsylla$ $pyricola$ (Hemiptera: Psyllidae), is a serious insect pest of commercial pear crops. The species, which resides on pear trees throughout its life cycle, is rapidly spreading in some regions of the world. The population genetic structure of the species collected from several pear orchards in Korea was studied to understand the nature of dispersal and field ecology of the species. The 658-bp region of mitochondrial COI gene and the 716-bp long complete internal transcribed spacer 2 (ITS2) of the nuclear ribosomal DNA were sequenced. Unlike other previously studied insect pests, the COI-based genetic diversity of the pear psylla was extremely low (maximum sequence divergence of 0.15%). This finding allowed us to conclude that the species may have been introduced in Korea relatively recently. ITS2 sequence-based analyses of phylogeny, population differentiation, gene flow, and hierarchical population structure all concordantly suggested that the pear psylla populations in Korea are neither genetically isolated nor hampered for gene flow. These genetic data are concordant with the dispersal of an overwintering winterform morph outside the non-pear habitat in the fall.