• 수산해양기술연구
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• 제32권3호
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• pp.266-272
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• 1996

The distribution and abundance of fish in the Cheju southeastern area was studied by the combined hydroacoustic and bottom trawl surveys in April 1994 and in July 1995, respectively. The main purpose of these investigations was to provide the basic data for this management and the biomass estimation of commercially important demersal fish stocks in this area. The hydroacoustic surveys were performed by using a 50 kHz scientific echo sounder system with a microcomputer-based echo integrator. Acoustical measurements of fish abundance and distribution were conducted along the cruise tracks of research vessel and during all trawl hauls by continuous echo sounding. The average weight-normalized target strength for demersal fish aggregations was derived from the relationship between the mean volume backscattering strength for the depth strata of trawl hauls and the weight per cubic meter of trawl catches. The geographical distribution of fish stocks in the 1994 survey area was investigated in relation to oceanographic conditions. The results obtained can be summarized as follows: 1. From the 1994 and 1995 survey data, the relationship between the mean volume backscattering strength (, dB) for the depth strata of trawl hauls and the weight (W, kg/$m^3$) per cubic meter of trawl catches was expressed by the following equation = - 32.8+ lOlog(W) The average weighted-target strength value at 50 kHz derived from this equation was .. 32.8 dB/kg. 2. In 1994 and 1995, both surveys showed a trend of decreasing fish abundance toward the southern area of the Cheju Island with high densities offish along the west coast ofth.e Tsushima Island. The highest demersal concentrations in the southern area of the CheJu Island appeared in bottom waters colder than $12^{\circ}C.$. . 3. From the results of combined bottom trawl and hydroacoustic surveys, the estunated fish densities in the southeastern area of the Cheju Island were 1.5488 x $10^-4$kg/$m^3$ in the 1994 surveyand 1.9498 x $10^-4$kg/$m^3$ in the 1995 survey, respectively.

• Imaging Science in Dentistry
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• 제36권2호
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• pp.95-101
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• 2006

Purpose : Bony strength is dependent on bone mass and bony structure. So this study was designed to investigate the relationship between the bone mass and bony trabecular characteristics. Subjects and Methods : Study subjects were 51 females (average age 68.6 years) and 20 males (average age 66.4 years). Bone mineral density (BMD, $grams/cm^2$) of proximal femur was measured by a dual energy X-ray absorptiometry (DEXA). Regions of interest (ROIs) were selected from the digitized radiographs of proximal femur. A customized computer program processed morphologic operations (MO) of ROIs. 44 skeletal variables of MO were calculated from ROIs on the Ward's triangle and greater trochanter of femur. WHO BMD classes were predicted by MO variables of the same ROI. Classification and Regression Tree analysis was used for calculating weighted kappa values, sensitivity and specificity of MO. Results : The discriminating factors of morphologic operation were branch point, branch point [per cm sq]. Age also played important role in distinguishing osteoporotic classes. The sensitivity of MO at Ward's triangle and Greater Trochanter was 91.8%, 65.6%, respectively. The specificity of MO was 100% at Ward's triangle and Greater Trochanter. Conclusion : Bony trabecular characteristics obtained using radiological bone morphometric analysis seem to be related to bone mass.

• 한국세라믹학회지
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• 제32권11호
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• pp.1269-1275
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• 1995

Effects of GeO2 addition on the thermal and structural stabilities of PbO-Bi2O3-Ga2O3 glasses were studied. Thermal stabilities, as assessed by the weighted thermal stability factors [(Tx-Tg)/Tg], increased with GeO2 concentraton from 0.097 to 0.210 with the addition of 20 mol% GeO2. Increasing GeO2 content resulted in the decrease of apparent density, molar volume, refractive index and thermal expansion. On the other hand, IR transmission cut-off (λT=50%) moved from 6.73${\mu}{\textrm}{m}$ for the ternary PbO-Bi2O3-Ga2O3 glass to shorter wavelength side, 5.98${\mu}{\textrm}{m}$ for a glass containing 20mol% GeO2. There were little change with GeO2 content, however, in the activation energies for the viscous flow of approximately 140 kcal/mole within the temperature interval of 300~50$0^{\circ}C$. Addition of GeO2 to PbO-Bi2O3-Ga2O3 glasses enhanced the thermal and structural stabilities significantly at the expense of their infrared transmittance. An appropriate compsomise between these two opposite trends should be made following the specifications of the final applications.

• Bulletin of the Korean Chemical Society
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• 제13권1호
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• pp.70-74
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• 1992

Two crystal structures of ethylene (a= 12.272(2) ${\AA}$) and acetylene (a = 12.245(2) ${\AA}$) sorption complexes of dehydrated fully $Ca^{2+}$-exchanged zeolite A have been determined by single crystal X-ray diffraction techniques in the cubic space group, Pm3m at $21(1)^{\circ}C$. Their complexes were prepared by dehydration at $360^{\circ}C$ and $2{\times}10^{-6}$ Torr for 2 days, followed by exposure to 200 Torr of ethylene gas and 120 Torr of acetylene gas both at $24^{\circ}C$, respectively. The structures were refined to final R (weighted) indices of 0.062 with 209 reflections and 0.098 with 171 reflections, respectively, for which I > 3${\sigma}$(I). The structures indicate that all six $Ca^{2+}$ ions in the unit cell are associated with 6-oxygen ring of the aluminosilicate framework. Four of these extend somewhat into the large cavity where each is coordinated to three framework oxide ions and an ethylene molecule and/or an acetylene molecule. The carbon to carbon distance in ethylene sorption structure is 1.48(7) ${\AA}$ and that in acetylene sorption structure 1.25(8) ${\AA}$. The distances between $Ca^{2+}$ ion and carbon atom are 2.87(5) ${\AA}$ in ethylene sorption structure and 2.95(7) ${\AA}$ in acetylene sorption structure. These bonds are relatively weak and probably formed by the electrostatic attractions between the bivalent $Ca^{2+}$ ions and the polarizable ${\pi}$-electron density of the ethylene and/or acetylene molecule.

• 대한영상의학회지
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• 제79권6호
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• pp.348-353
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• 2018

간의 가성 림프종은 비종양성 림프구의 절 외 과다증식에 의해 형성되는 드문 양성 종양이다. 검색한 바에 따르면 현재까지 영문으로 46예가 보고되었다. 우리는 75세 여자환자에서 과혈관성 종양으로 오인된 간의 가성 림프종 증례를 보고하고자 한다. 조직검사상 직장의 신경내분비 암종이 진단된 후 시행한 조영증강 전산화단층촬영에서 1.0 cm 크기의 경계가 불분명하고 낮은 감쇄를 보이는 결절이 간에 관찰되었다. 자기공명영상에서는 동맥 조영기에 조영 증강을 보이고, 20분 지연기 조영 영상에서 저신호 강도를 보이며, 확산강조영상에서 고신호 강도를 보였다. Fluorodeoxyglucose (이하 FDG) positron emission tomography (PET)/CT에서는 FDG의 섭취 증가를 보였다. 초음파에서는 저에코성 병변으로 관찰되었고, 초음파 유도 하 조직검사를 통하여 간의 가성 림프종으로 확진 되었다.

• 한국정보통신학회논문지
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• 제24권4호
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• pp.474-480
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• 2020

최근 4차산업 혁명의 시대가 도래하면서 새로운 기술들이 많이 구현되고 있는 추세이다. 그 중 영상신호는 다양한 분야에서 활용되어 지고 있다. 하지만 영상신호를 송,수신할 때 다양한 이유로 잡음이 발생하게 되며 Salt and Pepper 잡음과 AWGN이 대표적이다. 영상처리를 수행 할 때 잡음을 제거하지 않고 처리하게 되면 오류의 전파라는 문제점을 야기할 수 있다. 일반적으로 잡음을 제거하는 방법으로 CWMF, MF, AMF 등이 있지만 이러한 필터들의 경우 고밀도 잡음 영역에서 다소 미흡한 성능을 보이며, 스무딩 현상으로 인해 에지 성분의 보존률도 다소 떨어진다. 본 연구에서는 표준편차를 이용한 변형된 가중치 필터를 이용하여 Salt and Pepper잡음을 효과적으로 제거하는 알고리즘을 제안한다. 제안한 알고리즘의 잡음 제거 성능을 입증하기 위해 PSNR과 확대영상을 사용하여 기존의 알고리즘과 비교하였다.

• Journal of Radiation Protection and Research
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• 제45권4호
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• pp.171-177
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• 2020

Background: This study aims to determine the effective atomic number (Zeff) from dual-energy image sets obtained using a conventional computed tomography (CT) simulator. The estimated Zeff can be used for deriving the stopping power and material decomposition of CT images, thereby improving dose calculations in radiation therapy. Materials and Methods: An electron-density phantom was scanned using Philips Brilliance CT Big Bore at 80 and 140 kVp. The estimated Zeff values were compared with those obtained using the calibration phantom by applying the Rutherford, Schneider, and Joshi methods. The fitting parameters were optimized using the nonlinear least squares regression algorithm. The fitting curve and mass attenuation data were obtained from the National Institute of Standards and Technology. The fitting parameters obtained from stopping power and material decomposition of CT images, were validated by estimating the residual errors between the reference and calculated Zeff values. Next, the calculation accuracy of Zeff was evaluated by comparing the calculated values with the reference Zeff values of insert plugs. The exposure levels of patients under additional CT scanning at 80, 120, and 140 kVp were evaluated by measuring the weighted CT dose index (CTDIw). Results and Discussion: The residual errors of the fitting parameters were lower than 2%. The best and worst Zeff values were obtained using the Schneider and Joshi methods, respectively. The maximum differences between the reference and calculated values were 11.3% (for lung during inhalation), 4.7% (for adipose tissue), and 9.8% (for lung during inhalation) when applying the Rutherford, Schneider, and Joshi methods, respectively. Under dual-energy scanning (80 and 140 kVp), the patient exposure level was approximately twice that in general single-energy scanning (120 kVp). Conclusion: Zeff was calculated from two image sets scanned by conventional single-energy CT simulator. The results obtained using three different methods were compared. The Zeff calculation based on single-energy exhibited appropriate feasibility.

• Journal of information and communication convergence engineering
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• 제20권1호
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• pp.22-30
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• 2022

The reinforcement learning algorithm has proven its potential in solving sequential decision-making problems under uncertainties, such as finding paths to route data packets in wireless sensor networks. With reinforcement learning, the computation of the optimum path requires careful definition of the so-called reward function, which is defined as a linear function that aggregates multiple objective functions into a single objective to compute a numerical value (reward) to be maximized. In a typical defined linear reward function, the multiple objectives to be optimized are integrated in the form of a weighted sum with fixed weighting factors for all learning agents. This study proposes a reinforcement learning -based routing protocol for wireless sensor network, where different learning agents prioritize different objective goals by assigning weighting factors to the aggregated objectives of the reward function. We assign appropriate weighting factors to the objectives in the reward function of a sensor node according to its hop-count distance to the sink node. We expect this approach to enhance the effectiveness of multi-objective reinforcement learning for wireless sensor networks with a balanced trade-off among competing parameters. Furthermore, we propose SDN (Software Defined Networks) architecture with multiple controllers for constant network monitoring to allow learning agents to adapt according to the dynamics of the network conditions. Simulation results show that our proposed scheme enhances the performance of wireless sensor network under varied conditions, such as the node density and traffic intensity, with a good trade-off among competing performance metrics.

• Advances in aircraft and spacecraft science
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• 제8권4호
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• pp.345-372
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• 2021

The analysis of nonlinear vibrations, buckling, post-buckling, flutter boundary determination and post-flutter behavior of a homogeneous curved plate assuming cylindrical bending is conducted in this article. Other assumptions include simply-supported boundary conditions, supersonic aerodynamic flow at the top of the plate, constant pressure conditions below the plate, non-viscous flow model (using first- and third-order piston theory), nonlinear structural model with large deformations, and application of mechanical and thermal loads on the curved plate. The analysis is performed with constant environmental indicators (flow density, heat, Reynolds number and Mach number). The material properties (i.e., coefficient of thermal expansion and modulus of elasticity) are temperature-dependent. The equations are derived using the principle of virtual displacement. Furthermore, based on the definitions of virtual work, the potential and kinetic energy of the final relations in the integral form, and the governing nonlinear differential equations are obtained after fractional integration. This problem is solved using two approaches. The frequency analysis and flutter are studied in the first approach by transferring the handle of ordinary differential equations to the state space, calculating the system Jacobin matrix and analyzing the eigenvalue to determine the instability conditions. The second approach discusses the nonlinear frequency analysis and nonlinear flutter using the semi-analytical solution of governing differential equations based on the weighted residual method. The partial differential equations are converted to ordinary differential equations, after which they are solved based on the Runge-Kutta fourth- and fifth-order methods. The comparison between the results of frequency and flutter analysis of curved plate is linearly and nonlinearly performed for the first time. The results show that the plate curvature has a profound impact on the instability boundary of the plate under supersonic aerodynamic loading. The flutter boundary decreases with growing thermal load and increases with growing curvature.

• 한국정보통신학회논문지
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• 제25권12호
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• pp.1846-1852
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• 2021

현대 사회는 4차 산업혁명과 IoT 기술의 발전으로 폭넓은 분야에 다양한 디지털 기기들이 보급되고 있다. 하지만 영상을 획득하거나 전송하는 과정 등에서 잡음이 발생하여 정보를 훼손할 뿐 아니라, 시스템에 영향을 끼쳐 오류와 잘못된 동작을 일으킨다. 영상 잡음 중 대표적인 잡음으로 AWGN이 있다. 잡음을 제거하기 위한 방법으로 선행연구가 진행되어져 왔고 그 중 대표적인 방법으로 AF, A-TMF, MF 등이 있다. 기존의 필터들은 영상의 특성을 고려하기 어려워 고주파 성분이 많은 영역에서는 스무딩 현상이 발생한다는 단점이 있다. 따라서 제안한 알고리즘은 고주파영역에서도 효과적으로 잡음을 제거하기 위해 표준편차 분포도를 구한 후, 커브 피팅 방식을 이용한 라플라스 분포의 확률밀도함수 가중치를 적용하여 최종 출력을 구한다.